Integrated Reservoir Mapping while Drilling through High Definition Deterministic Inversion Enhances Horizontal Well Optimization.

A compositional equation-of-state simulator has been used to make comparisons of CO2 process performance with several combinations of horizontal and vertical wells and various alternative reservoir descriptions. This is the first time that the performance of CO2 flooding using horizontal wells has been reported. We have used the reservoir and fluid properties of an actual West Texas carbonate reservoir that is currently being waterflooded. The phase behavior and properties of the CO2 used in these simulations are typical of those of multiple-contact- miscible field conditions of West Texas. A layered-type reservoir description was initially used to investigate the effect of water- altemating-gas (WAG) ratio with various combinations of well types. We then investigated the effect of vertical permeability, length, and position of the horizontal injector using the same reservoir description and a horizontal injector-vertical producer combination. Similar investigations using an unconditioned stochastic permeability field having a Dykstra Parsons coefficient (VDP) of 0.81 were made. Our final three-phase flow simulation was performed using a stochastic permeability field conditioned with core data. Since three nonaqueous phases can occur at low temperatures typical of West Texas floods resulting in up to four-phase flow with mobile water, we investigated the impact of four-phase flow in one of these simulations. This is the first time that three-dimensional, four-phase flow reservoir simulations have been reported with either vertical or horizontal wells.

The underbalanced drilling of horizontal wells involves the injection of gas either with the drilling mud or via a separate string to that through which the drilling mud is injected. Nitrogen is generally used to prevent fire and explosion hazards during drilling; however, this adds considerably to the cost. Costs can be reduced by the replacement of nitrogen injection with normal air, de-oxygenated air or vitiated air (air/nitrogen mixture), but this increases the potential for flammable, or explosive, mixtures to be present in the wellbore and surface piping during underbalanced drilling. Safe operational ranges of oxygen-containing drilling mud mixtures can be determined if the flammability of the mixtures is known. Several studies were carried out to determine the flammability of these mixtures as a function of pressure to minimize the potential for downhole and surface explosion, and to set out the guidelines for safe underbalanced drilling operations of horizontal wells. A specially-designed apparatus was calibrated utilizing methane/air mixtures, then the ignition and the flammability characteristics of various mixtures of air, drilling mud and live oil were established over a range of pressures from atmospheric to 2,100 kPa at 21 ° C. Additional tests were carried out utilizing drilling mud, live oil, and either a nitrogen/air mixture (vitiated air) or de-oxygenated air. Flammability limits were determined for each series of experiments, and the results used to design the safety features for the underbalanced drilling of several horizontal wells. The field trials proved successful, and significant cost savings were realized. Introduction A growing demand for maximizing heavy oil production in a cost-effective manner has led to the development of a variety of novel technologies. One such technology involves the drilling of wells employing underbalanced or near-balanced drilling procedures in order to minimize the possibility of formation damage due to drilling fluid invasion. There is a potential for flammable, or explosive, mixtures to be present in the wellbore and surface piping during this type of drilling operation. In underbalanced drilling, normal air or an oxygen-containing gas (usually vitiated air, which is air mixed with nitrogen, or de-oxygenated air, which is air with some of the oxygen removed) is injected and/or circulated with the drilling mud to reduce the potential for formation damage due to whole mud, fluid filtrate and solids invasion into the hydrocarbon-bearing formation. The study presented in this paper was performed to determine the safe conditions for underbalanced drilling of Husky Wainwright Well 15B-31-44-4 W4 using compressed air and liquid nitrogen. This well, located in the Camrose reservoir, which is a fractured vugular carbonate at 690 m TVD, was proposed to be drilled 550 m laterally(1). The main objectives of this investigation were:To establish the flammability of mixtures of air, live heavy oil and drilling mud as a function of pressure, andTo determine the optimum composition of vitiated air (nitrogen- air mixture), based on the flammability data, in order to minimize the potential for ignition or explosion during the underbalanced drilling operation.

The horizontal wells within the context of this case study are located offshore Malaysia, where the reservoirs vary in grain size and quality. The infill wells include 3 oil producer wells targeting S reservoir and 1 horizontal sidetrack well targeting R1-R3 subunit reservoirs. The horizontal wells’ objective is to optimize minimum lateral length of 1,000-2,000ft MD at 1/3 vertical standoff from GOC within the target oil column. Based on recent data from offset wells, the fluid contacts (GOC and OWC) remained uncertain, hence well placement within the target oil column becomes the main challenge. The wells are expected to have low resistivity contrast between oil and water composition. In this kind of reservoir environment, the standard reservoir mapping tool may not be sufficient for differentiating reservoir fluid properties of oil and water bearing formation. For such challenging condition, an integrated real-time well placement technology, high tier triple-combo logs, Neutron Near- Far count and Formation Sigma measurements were deployed to fully achieve drilling objectives. 3 horizontal wells with 1 horizontal sidetrack well were successfully executed within the target zone, achieving objectives beyond expectation. A new generation of LWD tool including high-definition reservoir mapping-while-drilling technology with advanced inversion was deployed to fulfill geosteering requirements. The workflow presented in this project is a synergized scope of multi-domain, from both drilling and subsurface. This case study demonstrated the value of high-definition reservoir scale mapping technology. It provides an innovative and deterministic method to identify low resistivity low contrast boundaries of oil from transitional water zone which was difficult to be achieved by conventional reservoir mapping tool. At the landing section, the high-definition tool helped to reveal clearly OWC below the tool with greater confidence compared to the standard tool. The information from the high-definition tool, paired with the fluid identification offered from Neutron-Density and Neutron Near- Far count together were essential for an accurate landing. The usage of reservoir scale mapping technology in the horizontal section revealed the tilted OWC and reservoir structure at the same time, which allowed the team to achieve the required minimum production length while maintaining required standoff from the OWC. All wells were geosteered successfully with the accomplishment of placing the trajectories in optimum positions despite having a tight TVD window.

High water production is a major issue in horizontal oil wells, especially in longer laterals, because of the high drawdown from the heel to toe. In addition, the presence of heterogeneity along the lateral section can lead to uneven sweep of hydrocarbons which can result in poor recovery. To control the water production and achieve better sweep efficiency, ICDs have been introduced which balance fluid flux along the producing horizontal well. This paper discusses the feasibility and results of using integrated technologies such as ICDs along with rotary steerable drilling systems (RSS) and azimuthal logging while drilling well placement technology to achieve higher reservoir sweep efficiency. This case study is focused on a Gulf of Mexico (GoM) shelf horizontal well which was completed with prepacked screens. The well was sanded in and plugged after five years of high water production. A saturation log was run in the offset well which granted the viability to revisit this reservoir. Consequently, a new offset horizontal well was proposed and drilled next to the existing well to sweep out remaining reserves. For the new offset well, full field dynamic simulations were performed to evaluate attic placement methodology and optimization of Inflow Control Devices (ICDs) into the integrated design. The results illustrate that attic horizontal well placement is feasible using integrated drilling with ICD technology to maximize the sweep efficiency.

Length and profile shape of horizontal section of the production well is one of the main issues in the justification of horizontal well completion. Justified choice of horizontal well completion and profile design is based on the main objectives: provide high initial rate, maximize the cumulated gas and condensate production, reduce the risk of well drilling and completion, extend a period with water free production, hence resulted in the maximum NPV. The main factors that influence the choice of horizontal well profile are the geological structure of the productive formation, its reservoir properties, the location of formation fluid contacts, formation anisotropy, the ratio of vertical and horizontal heterogeneity. In this paper we investigate the influence of mentioned geological factors on the choice of horizontal well profile. Various profiles of horizontal wells- directional, horizontal and U-shaped have been considered for gas condensate reservoirs. The analysis was conducted on the basis of hydrodynamic modeling Eclipse 300 using a function of multi-segment well. After choice of the optimal length for the horizontal section of the well, a simulation was performed. Also there was a comparison of the performance for directional and U-shaped horizontal wells with the same length. During comparing the well performance well productivity, cumulative gas and condensate production, inflow profiles, the conditions of liquid removing from well bottom of were evaluated. Sensitivity evaluation of the optimal profile selecting to the reservoir permeability and its anisotropy was performed. It helps to take into account the effect of uncertainty on the performance of the well. Selecting a profile of the horizontal section of the well is one of the main issues in the design and affects not only the final gas and condensate recovery, but also helps to clarify the geological structure formation during logging, and enable the development of all productive layers, reduce the risk of complications during the operation. Structural features of horizontal wells unlike allow to obtain vertical flow rates several times superior performance of vertical wells. And the increase in horizontal wells is provided not by increasing the drawdown, and by increasing the filter surface. Productivity is limited in the vertical wells of the reservoir reveals the thickness, whereas the thickness of a predetermined value for the formation and drawdown -the geometrical parameters of the liner and, consequently, horizontal wells depends on the length of the horizontal wellbore. The horizontal wellbore completion may be regarded as an effective method for production of hydrocarbons, and as a method of stimulation. Engineering and technology horizontal drilling, completion fluid, their performance, conduct work under stimulation to them, economic indicators drilling and operation of horizontal wells devoted several thousand research. At the same time question the justification of the optimal design and the length of the gas and gas condensate wells are virtually unexplored. Studies on this topic have been done by Z.S. Aliyev, V. Sheremet and V.A. Chernykh. Z.S. Aliyev in one of his works says that the only way to study the optimal design of horizontal gas wells drilled in inhomogeneously layered strata, is a numerical solution to this problem through the creation of geological and mathematical models of fragments of such deposits and the joint solution of unsteady, multidimensional, multiphase and multicomponent filtering the horizontal trunk with the equation of motion with a variable flow rate of the mixture along the length of the barrel. In this paper we provide a rationale for completing horizontal wells for specific geological conditions of the N-th gas condensate field located in the east of the autonomous area.

The Mumbai Offshore region of Western Offshore India is characterized by geologically complex reservoirs, where oil zones are bounded by variable Gas-Oil Contacts (GOC) and Oil-Water Contacts (OWC). Accurate delineation of these fluid contacts is essential to successfully land horizontal wells within productive zones. However, lateral variability in contact positions often introduces significant uncertainty. Conventionally, operators mitigate this uncertainty by drilling pilot holes to confirm fluid levels, followed by sidetracks to optimize landing 2m below GOC. While effective, this approach adds considerable cost, time, and risk without guaranteeing that fluid contacts remain consistent along the planned lateral section. This paper presents a case history demonstrating the successful application of high-definition look-ahead reservoir mapping using Ultra Deep Azimuthal Resistivity (UDAR) technology as a replacement for the conventional pilot hole strategy. The UDAR tool provides deep resistivity measurements with azimuthal sensitivity and advanced inversion capabilities, enabling proactive mapping of formation boundaries and fluid contacts ahead of the bit. A feasibility study was conducted based on offset well data and geological characterization of the target reservoir. The study indicated that UDAR could reliably detect resistivity contrasts associated with both GOC and OWC at prior depths sufficient to make landing decisions and mitigate contact uncertainty. During operations, UDAR was deployed in a triple-combo bottom hole assembly (BHA), allowing real-time resistivity inversions to update subsurface models dynamically. The technology successfully mapped the GOC several meters ahead of the bit during the landing phase, enabling the well trajectory to be adjusted proactively. The OWC was consistently mapped from entry into the reservoir. Both the GOC & OWC were mapped along the length of the landing section and were found to vary in position consistent with the data from the offset wells. UDAR's look-ahead capability mitigated fluid contact uncertainties and achieved the landing objectives, marking a significant advancement in drilling efficiency and cost reduction. This case history represents a significant advancement in reservoir navigation practices in Western Offshore India. It demonstrates the technical viability and operational benefits of deploying high-definition look-ahead resistivity mapping to replace conventional pilot hole methods. Beyond improving drilling efficiency and reducing costs, the approach provides a robust framework for managing geological uncertainty in complex reservoirs. The successful outcome establishes a benchmark for future offshore wells where precise contact mapping and optimal landing are critical to unlocking production potential.

Improvements in horizontal drilling technology made it possible to drill almost in all types and shapes of reservoirs. No change, however, was made in the design of drill pipes to overcome the high stresses especially for drill pipe rotating in medium or short radius horizontal wells. During drilling of some horizontal wells in the Middle East area, an abnormal amount of tubular failure was noticed in the drill string being used. This paper presents a field case study of drill string failure during drilling of medium radius horizontal wells. Investigations as well as a metallurgical evaluation were conducted in an attempt to establish the possible causes of the drill string failures. Other possible reasons for drill string failures and suggestions to minimize the bending stress of drill pipes are also discussed.

The CD carbonate of the Ngimbang formation in the X-Field, East Java Basin, has multiple reservoir targets with varying flow units due to secondary porosity from karst processes. Each of these reservoirs are thin, and the continuity of the karst within the reservoir is quite random. The amount of producible hydrocarbon will depend on the length of the drain section along the reservoir and the amount of karst intersected by the wellbore trajectory. Thus, maintaining the trajectory inside the carbonate reservoir while mapping and targeting the karst position is especially important for hydrocarbon productivity. Many horizontal and high-angle wells were drilled from the first offshore platform in this field as part of the phase one development plan. To maintain production in the field, a new offshore platform was placed south of the first platform, targeting new development areas in the field. Five horizontal wells were planned as part of the second development phase. The first horizontal well to be drilled in the second phase was the most challenging well because of the high uncertainty in the structural dips along the lateral length caused by the low-seismic resolution data and the limited number of nearby offset wells for control points. Moreover, the offset wells had inconsistent log properties, which complicates for correlating the well landing in the targeted karst level within the reservoir. Initially, a pilot hole was planned to reduce the landing uncertainties; however, drilling the pilot hole was being challenged for cost efficiency. As a result, a geosteering strategy was proposed instead, comprised of landing and geosteering using a new logging-while-drilling (LWD) combination of a new high-definition reservoir mapping technology, high-resolution laterolog borehole imaging technology, and multifunction LWD tool. This paper presents the complete preparation procedure of the geosteering project, strategy, and evaluation using this new LWD combination for improved reservoir interpretation. The deeper reading and higher resolution of the new reservoir mapping technology enabled continuous mapping of the target reservoir boundaries that reduced the structural uncertainties in the seismic measurements, and for the first time, revealed the karst architecture within the reservoir with greater details. This high-definition information helped to land the well precisely in the target karst sweet spot, improved the understanding of the karst characters along the trajectory, and provided greater confidence in the real-time geosteering decision. The high-resolution borehole image revealed the carbonate rock texture and karst and vugs appearance on a smaller scale, which was used to analyze the secondary porosity distribution and contribution along the wellbore trajectory. Integrating this additional information while drilling allowed for bridging the gap from seismic to reservoir scale, and finally linking the information to the high-resolution borehole image for improved geological understanding; therefore, improved geosteering strategy in the field.

REVITALIZATION OF A MATURE VOLATILE AND CONDENSATE OIL RESERVOIR USING HORIZONTAL WELLS. Abstract The great interest shown in optimizing the exploitation of reservoirs, in the last two decades through the drilling of horizontal wells, has been the best evidence of the potential of this technology. Significant increments in production rates and recoveries have been reported even in oil fields considered uneconomic. In this paper, the revitalization of the RG-14, COEF reservoir in the Santa Rosa Field by means of horizontal wells is analyzed. This reservoir is the most important mature reservoir producing volatile oil and condensate in Eastern Venezuela. The RG-14, COEF reservoir started its production in April of 1950, having been subjected to gas injection since 1955. Depth of the reservoir varies from 6560 ft subsea at the crest of the dome to 11150 ft at the flank. Presently, gas channeling and the subsequent entrampment of oil in undrained areas limit the recovery of 14.5 MMBls of remaining reserves. Consequently, the drilling of horizontal wells is a potential option to minimize gas channeling and maximize the drainage area, increasing crude production, final recovery and the economic feasibility of the project, at the same time. This paper presents the integration of geological, reservoir and production studies to define undrained flow units, the selection of objective areas for three horizontal wells, the characterization of fluids, production forecast by means of pseudocompositional simulation and an economic analysis. A Peng-Robinson equation-of-state was used, to characterize both gas condensate and black oil. The simulation studies were performed only in the areas were horizontal wells are proposed, in order to compare them with vertical wells. Results indicate that it is feasible to reactivate production from the RG-14, COEF reservoir in the Santa Rosa Field from the current 567 STBD to a level of 2620 STBD through the drilling of three horizontal wells. Introduction In Corpoven's Anaco and San Tome traditional areas in the Eastern Venezuela Basin, there are about 134 mature fields of condensates and medium and light oil which still have reserves of between 50 and 300 million barrels. Secondary recovery processes (gas injection) used in these fields for the last 30 years have permitted the extraction of 75% of the initial estimated reserves. However, a good portion of the remaining reserves are still trapped due to inefficient drainage and preferential channeling of injected gas and/or water in the reservoirs subjected to a pressure maintenance. Due to these circumstances, the use of the horizontal drilling technology is required in order to maximize the contact with undrained areas and so reduce the water and/or gas coning. Consequently, this procedure will permit the acceleration of the final recovery of reservoirs. P. 231

With the advent of rotary steerable systems, successful drilling of horizontal wells became a reality in the oilfield. Even though the costs are much higher than for a vertical well, the production factor can be enhanced multiple times, making it very attractive. However, the drilling of horizontal wells is extremely difficult, mainly due to lateral lithological discontinuities of the reservoirs and seismic uncertainties. To overcome such challenge, Well Placement technique is used to interactively position the well based on geological and seismic criteria together with LWD measurements. While covering drilling, geology and geophysics, most Well Placement approaches rarely consider reservoir engineering aspects. Therefore the project objectives were to evaluate the impacts in the productivity generated by the geometrical changes in the trajectory through numerical reservoir simulation. The research work was then divided into two parts. The first one was the creation of a representative 3D synthetic reservoir model where numerical simulations were applied for each trajectory design. A detailed sensitivity analysis was made by comparing the results among the different trajectory cases in order to identify the relationship between well positioning and its productivity response. The second part consisted of a real geosteering case study. Around both planned and executed wellbores, it was created a detailed reservoir model enhanced by LWD inputs. To increase prediction accuracy, a refined gridding with variable cell size technique was applied to enhance pressure and saturation sensitivity. The level of precision was improved by using LWD measurements, such as the most precise formation pressure, the permeability near wellbore and the remote boundary mapper technology that provided a detailed reservoir structure based on formation resistivity contrast. Afterwards, reservoir simulations were performed in order to evaluate the impacts caused by the trajectory variations, demonstrating the expected productivity results versus the actual ones. The work delivers a novel ability to construct optimal horizontal wells not only by including conventional Well Placement technique, using geological and geophysical criteria, but also by adding into the workflow an advanced numerical simulation approach. Such integration allows the operator to predict the impacts on the productivity as the trajectory is being changed, and the actual reservoir geometry and its properties are determined by LWD measurements. It also reinforces that predictions related to reservoir productivity should not only be performed on planning stage, but most importantly during or right after well execution using relevant inputs, such as the actual well path, LWD logs, and formation pressure measurements, which all combined provides an enhanced reservoir model, and so a more accurate forecast analysis.

Tapping the remaining oil with horizontal wells is routinely used in high water-cut oilfields. However, it faces serious challenges in complex fluvial reservoirs with stacked sand body, horizontal interlayers, lateral barrier and complex water flooding conditions. Moreover, the depth uncertainty of the target interval, limited number of offset wells, rapid change of thickness, thin target intervals, and variable fluid contact have also increased the risks of the horizontal well placement. In order to locate the optimal positions of the horizontal wells, get the maximum recovery, reduce the risk of water flooding, minimize the drilling time, we propose a comprehensive well planning and optimization method based on multidisciplinary innovative techniques. New techniques from geology, geophysics, and drilling engineering are assembled to efficiently perform the challenging task. Firstly, an improved interwell 3D correlation technique was proposed to characterize the single sand body. The technique can depict the vertical hierarcy of reservoir. Secondly, we propose a lateral boundary delineation technique based on seismic geometrical attribute. Combined with ant tracking algorithm, we are able to extract the 3D lateral discontinuous surfaces. Based on above technique, we can build detailed architecture model fast and optimize the positions of horizontal wells. Considering the geological uncertainty, the boundary mapping tool is used to optimize the well trajectories in real time to avoid the water flooded zone and shale zone, and to stay in the sweet zone. We applied the integrated workflow in Q oilfield in Bohai Bay basin, East China. 112 horizontal wells are drilled. The drilling results proved that boundary mapping tool can achieve smooth landing of well path and delineate the accurate geometry and thickness variation of sand body which reduces the depth uncertainty of seismic horizon explanation, and keeps the horizontal well trajectories away from oil-water contact. The production results show that 86% horizontal wells have achieved low water-cut and high oil production rate. The total production rate of Q oil field has increased by 2.5 times.

This scientific work summarizes the experience of drilling horizontal wells at abnormally high reservoir pressures in the Western part of Turkmenistan. The article describes in detail the choice of the layout of the bottom-hole assembly (BHA), drilling methods, the area of the angle set and the stabilization interval of the zenith angle, and also notes the importance of the quality of drilling mud when drilling horizontal wells. The work performed proves that drilling of horizontal wells is possible both at an early and late stage of field development and their drilling should be provided for when creating technological development schemes at the level of the field development project. Such work will find application for drilling deep horizontal wells with abnormally high reservoir pressures and will lead to an increase in hydrocarbon production, as well as organizational restructuring of horizontal drilling on a scientific basis. Keywords: oil recovery; geological structure; deviation; zenith angle; borehole; communication channel.

The prediction and optimization of the rate of penetration (ROP) for horizontal wells are more complicated than for vertical wells, but most of the current ROP prediction studies are for vertical wells, which cannot be adapted to the complex drilling characteristics of horizontal wells. To this end, this paper proposes a data knowledge dual-driven horizontal well ROP prediction method. Firstly, the drilling characteristics of horizontal wells are analyzed, showing that the horizontal wells ROP prediction model cannot be modeled using surface measurement data; secondly, based on the analysis of horizontal well drilling characteristics, a physical model-based horizontal well ROP modeling data pre-processing method is proposed by introducing the drag and torque model. Finally, a data knowledge dual-driven horizontal well ROP prediction method is proposed in conjunction with data-driven algorithms. The proposed horizontal well ROP prediction method is applied to the A1~A4 wells in the Sichuan area. Compared with the conventional data-driven ROP prediction method, the prediction accuracy of this method is improved by 30%. The proposed method can provide a basis for the intelligent optimization and management of ROP during the drilling of horizontal wells.

A new multi-disciplinary integrated steering technology for horizontal wells in tight sandstone gas reservoirs: A case study of the Ordos Basin

Recent advancements in technologies pertaining to the drilling of horizontal well and multistage hydraulic fracturing have made it possible to get significant hydrocarbon production even from extremely low permeability formations. Evaluation of the economics is becoming increasingly essential before committing to any big investment. In this scenario, production forecasting plays an important role by not only evaluating the economic feasibility of the project, but also helping in the selection of the most optimal development strategy (Shivam et al. 2017). This paper presents an integrated workflow that has been applied in one of unconventional gas bearing formation which is a common reservoir in Egypt’s Western Desert. It does form a reasonable reservoir size and spread over several hundred sq.kms. It is characterized as a low permeability carbonate (0.2 mD) in soft chalk reservoir. Many vertical wells were drilled and completed in the appraisal program for collecting the required data to evaluate reservoir performance before the completion of horizontals, but economical target production rates could not be achieved. To help optimize field development strategy and further increase production, a full field development plan was initiated by drilling horizontal wells with multistage fracturing stimulation. Horizontal pilot wells were drilled and completed along and perpendicular the minimum horizontal in-situ stress direction to enable both transverse and longitudinal fracture propagation patterns for the best completion option. The objective of this paper is to present an integrated approach to evaluate an unconventional resource, improve the completion efficiency, improving the future fracture design and understand the productivity enhancement specifically in the Western Desert of Egypt, through a detailed analysis of production data and pressure transient analysis. The conclusions from this study will help in evaluating the behavior of multistage fractured horizontal with different fracture azimuth direction and generate production forecast for different development scenarios. The stimulated rock volume estimation will help in planning the future fracture design to increase well EUR. The proposed workflow and lessons learned formed the basis for subsequent development of various unconventional plays in Egypt.