Norwegian Trotting Association

Drilling fluids are very complex and are essential for safe and efficient drilling operations. It is vital for the drilling operator to be able to select an appropriate fluid for each individual well, including the decision of using oil-based or water-based fluids or “muds” (OBM or WBM). In this article we present results from a comparative study of three OBM’s which are based on the same fluid system (Versatec). This work is part of a larger investigation where the main objective is to identify and evaluate the difference in the hole cleaning capabilities of OBM’s and WBM’s with similar viscosity as measured by the API/ISO standards. This paper describes an experimental investigation of cuttings transport using flow loop laboratory tests without and with injected cuttings size particles using various industrial oil based fluids with varying density and viscosity. The flow loop includes a 10 meter long test section with 2″ OD free whirling rotating steel drillstring inside a 4″ ID wellbore made of concrete elements positioned inside a steel tubing. Sand particles were injected while circulating the drilling fluid through the test section. Experiments are conducted at atmospheric conditions, but are otherwise designed to represent downhole conditions as closely as possible with respect to fluid and particle properties, flow rates and geometry. Fluids are tested at different flow rates with and without rotation of drill string, with and without sand injection. This has allowed us to study the effects of flow rate and drill string rotation on hole cleaning capabilities of different fluids. The primary results are pressure drop, steady state sand bed height in a horizontal annulus versus fluid and cuttings rates for rotating and non-rotating drill string and in particular the critical rates for fully suspended flow. The results are interpreted in light of results from laboratory characterization of the same fluids, conducted as part of the same project. The results will increase understanding of the relationship between drilling fluid properties and hole cleaning performance. This will enable the development of improved drilling fluids, both operationally and environmentally. Such know-how will also be important in order to develop more accurate transport models.

Abstract A well documented path to improving overall efficiency in project execution is through an integrated team approach which involves both the operator and the service suppliers. This paper describes what can be achieved when such a team adopts a fearless approach to new technology, and dares to think outside existing conventions. To be more specific, the paper covers the engineering, planning, and execution of a HTHP exploration program in the central North Sea by a Norwegian operator. Large areas of the North Sea contain the Cretaceous period of sediments which comprise of a massive hard layer of chalk that historically has posed a major drilling risk and expense to operators in the area. To mitigate expected problems an integrated team was gathered to thoroughly analyze drilling records and lessons learned from previous offset wells and re-engineer the drilling process with the aim of minimizing cost and uncertainty when drilling the most challenging chalk interval. The paper presents the hypothesis that formed the basis for the team effort, and the measures implemented based on said hypothesis. This includes an unconventional bit selection and the use of modern vibration measurement technology and mitigation techniques, as well as a key electro-mechanical modification of the advanced logging and directional suite completed by the lead service provider. The discussion and reasoning behind each step is included and the method was repeated in several wells with the same results, verifying the validity of the findings and making the paper a valuable input for drilling hard chalk. The nominal result from applying the new methodology was a doubling of the rate of penetration (ROP) in the harder layers, and the entire section of problematic strata was drilled in one single bit run. Drilling time was reduced by 12 days when compared to average figures from recent offset wells representing an estimated cost saving of 15 - 20% on the overall well budget. The method and savings presented are primarily of interest to stakeholders in the central North Sea, but can also be applicable to other areas with hard chalk and stringers with similar characteristics.

Abstract Deepwater corals (Lophelia) was identified in the vicinity of the location of the exploration well Pumbaa on the Norwegian Continental Shelf where a drilling operation was carried out by the GDF SUEZ E&P Norge AS (GDF SUEZ). When drilling in sensitive areas, it is a requirement from the Norwegian authorities that the operator shall monitor the drilling operation. Possible impacts on the corals were simulated prior to the drilling operation. In addition, monitoring of the discharges during drilling was carried out in order to document effects on the corals. The paper considers a comparison between measured and simulated discharges of drill cuttings and mud to the sea on the Pumbaa field in the Norwegian Sea. The actual monitoring program is presented in a separate paper on this conference (Moskeland et al. 2012). The main objective of the monitoring was to assess effects from the drilling activities on the corals south (and nearest) of the drilling location. The monitoring program included measurements of current, turbidity and sedimentation, as well as sampling of sediments from the seafloor. The data collected in the monitoring program turned out to be useful as well to validate numerical models for simulations of the discharges. In the present case, corals are located close to the drilling site, and the simulation tool could then be validated for prediction of potential exposure of the corals. The actual comparison between model simulations and measurements is carried out by comparing the actual depositions of barite on the sea floor. In addition, turbidity recordings close to the sea floor are compared with simulated concentrations of particle matter at the locations of the turbidity recordings. Good correspondence is obtained between model results and measurements on the occurrence of events of particle matter present in the water column at selected locations. A good similarity is found between measured/simulated depositions of barite at the sea floor, and measured/simulated concentrations of particle matter in the water column. Use of the model validated will strengthen the operator's ability to predict exposure (and consequently potential damage) on corals (and other biological resources) prior to the drilling operation. The operator may then obtain an "early warning" on exposure (potential damage). Measures can then be initiated to eliminate or reduce environmental impact.