Summary Observation of the sudden appearance of annular pressure in wells exposed to high temperature changes or excessive internal casing pressure prompted a laboratory investigation to simulate conditions under which cement sheath failure could occur and thereby define the causes, characteristics, and limits of the problem. Cement sheath failure is manifested by interzonal problem. Cement sheath failure is manifested by interzonal annular-fluid movement and abnormally high annular pressure at some point behind the casing up to and at the surface. Cement sheath point behind the casing up to and at the surface. Cement sheath failure can be observed in any producing area where excessive flowing temperatures exist at the surface or where excessive internal casing test pressures are used. The detrimental effects of cement sheath failure are numerous and may include lost revenue from lost production, potentially hazardous rig operations (especially when annular isolation loss creates shallow-water sands supercharged with gas), and potentially hazardous producing operations. Exposure of steel casing to excessive temperature increases or internal test pressures causes diametrical and circumferential casing expansion. This circumferential force creates a shearing force at the cement/casing interface, causing failure at the cement/casing interface or radial fracturing of the cement sheath from the inner casing surface to the outer casing (or borehole) surface.

Summary This paper presents a mechanism for filter-cake deposition by drilling fluids in laminar flow. The mechanism evolved from analysis of filtration-data plots obtained from two linear equations derived from filtration theory. With these plots, various fluid-loss additives were evaluated on their ability to form a low-permeability filter cake that can be eroded by a fluid in laminar flow. The mechanism was tested on two wells with high torque and drag, and the static API high-temperature/high-pressure (HTHP) values were minimized.

Summary A general method was developed to determine pore pressure in undercompacted shales on the basis of explicit relationships among measured shale properties, shale porosity, effective vertical stress, and pore pressure. Although calibration may be necessary, this technique neither uses empirical correlations nor requires establishment of normal trend lines. A modular approach allows users to implement custom equations. This paper outlines the concept and focuses on its application to real-time pore-pressure evaluation based on resistivity measurements.

Summary The Eunice Monument South Unit (EMSU) waterflood project is a large-scale (354 wells) example of implementing a waterflood in a highly depleted reservoir. Because of the maturity of this field (>50 years), several problems were encountered, such as drilling depleted intervals, corroded wellbores, and stimulating depleted and scaled-off formations. This paper discusses procedures to deal with these problems. Other topics discussed include infill drilling techniques, drilling and completion of high-volume water-supply wells, use of air/mist in drilling and deepenings, and water/CO2 injection equipment. By using existing techniques and implementing new ideas, we continually cut costs throughout the life of the project. Operations were improved through continuity, implementation and analysis of new techniques, and good communications. All improvements are documented with field results and show how continual monitoring and adjustments in operations can lead to an operationally efficient, cost-effective project.

Summary Since 1979, Esso Rep has drilled more than 150 exploration and development wells in the Paris basin. A cost-per-foot reduction of more than 40% was achieved despite a near doubling of rig rates. This paper discusses the unique directional drilling approach used and the drilling, formation evaluation, and contracting techniques.

Summary This paper deals with the planning, special equipment considerations, and operations necessary to convert 163 water injection wells to CO2 injectors that will function through at least the end of the century. The paper is divided into two parts: planning and engineering (wellhead, packer, and tubular selection) and procedural operation highlights (fishing, openhole cleanout, casing evaluation and repair, stimulation, liner running, wellhead replacement, packer setting, and the reworking of tubulars). A case-history approach was used to analyze the success or failure of the various methods and techniques used in this project. All 165 wells were converted as of March 29, 1989.

Summary For this study, we evaluated the stress distribution produced by moisture adsorption around a wellbore by applying the mechanics of deformable solids. This paper shows that the moisture-adsorption process is governed by a diffusion equation and that the equations governing the moisture-induced stresses around the hole are similar to those equations used in thermoelasticity. A computational method is developed for calculating the stress distribution around the borehole, and the experimental procedure for obtaining the material constants needed in the computation is presented. This paper also studies the effect of borehole pressure on the stress distribution around the hole. Results show that the magnitude and distribution of stresses around the borehole are very sensitive to the adsorption characteristics and the moisture-induced modulus change of the material.

Summary A compositional material-balance model was used to predict the densities of diesel- and mineral-oil-based muds at elevated pressures and temperatures. We measured the densities of diesel oil, two mineral oils, and calcium chloride solutions from 78 to 350°F and from 0 to 15, 000 psig. The measured densities were used in an existing compositional material-balance model to predict the densities of 11- and 17-lbm/gal oil-based muds. We also measured the densities of these muds at elevated pressures and temperatures and compared them with the predicted values. The results show excellent agreement between measured and predicted densities. The experimental density data were used to predict downhole densities and static wellbore pressures for the oil-based muds. Results show that the mineral-oil muds are not only more compressible than the diesel-oil muds, but also more susceptible to thermal expansion. Therefore, all the oil-based muds tend to give essentially the same static-wellbore-pressure profile.

Summary We investigated the behavior of casing pipe body and connections under simulated thermal recovery conditions. The study, performed in a new computer-controlled thermal-well simulator, examined the thermal stress behavior and leak resistance of pipe and connections at temperatures up to 354°C [670°F] under severe loading conditions similar to those encountered in thermal wells. We also studied the biaxial collapse resistance of the casing under the large axial tension that would exist after the cooling period in a steam-stimulation process. Results indicate that in a steam-injection process in which the casing is maintained at its maximum temperature for a period of time, stress relaxation can occur in a constrained production casing, resulting in the development of excessive tensile stress during the cooling period. Premium connections with metal-to-metal seals maintained gas leak resistance at temperatures up to 354°C [670°F], whereas the connections without metal seals did not. The biaxial collapse resistance of casing under large axial tension depended on the stress/strain characteristics of the material. Hot-rolled Grade K55 casing with work-hardening characteristics showed a biaxial collapse resistance higher than that predicted by the von Mises yield criterion. From results of this study, we concluded that heavyweight Grade K55 casing with premium connections is a good candidate for thermal well completions.

Summary With the movement of offshore rigs into deep water, the problem of gas hydrates has become an important issue in drilling. If a kick is taken, gas hydrates can form in the blowout preventer (BOP) or chokelines while the kick is circulated out. The water-based pill presented here significantly improves gas-hydrate inhibition. This pill, which can be spotted in the BOP and weighted up, is environmentally safe and easily adaptable to offshore operations. Compatible with commonly used drilling fluids, the pill can be mixed directly into the mud system without any adverse effects after the danger of hydrate formation diminishes. This technology is an important safety consideration for deepwater drilling well control and hydrate-free operations above the mudline.