This paper describes the application of particle size distribution principles for determining materials to be added to the mud system during casing while drilling operations. Casing while drilling (CwD) has been demonstrated to stop or significantly reduce lost circulation and improve wellbore strength. The mechanism by which this improvement occurs is not understood, however the results from this work significantly advance what is needed to get repeatable results. If wellbore strengthening can be systematically achieved, then wells can be drilled in known loss areas without contingency strings of casing. In addition, wells drilled in mature fields, where producing horizons have altered pressures either from depletion or pressure maintenance, can be drilled with fewer casing strings. Sidetracks become economical because hole size can be preserved for an effective completion and well costs are lowered by not using additional liners to reach the objective. By adding particles to the mud to fill in the particle size distribution, losses to natural fractures were stopped while directional wells were drilled with casing in the Piceance Basin of Colorado. Applying what was learned in a field trial of casing while drilling in the Alaskan Tarn Field, the open hole leak off resistance was improved by 3.0 pound per gallon (ppg) drilling with 7.0 inch casing in a 67 degree angled well. With this success, a four well casing while drilling campaign was executed with two wells drilled each in the Kuparuk and Tarn fields on Alaska's North Slope. Results were positive for 7.0 inch and 7.625 inch casings but wellbore strengthening did not occur sufficiently in the 5.50 inch casing trials. Annular clearance appears to be a critical component to success and is not yet fully understood. The results demonstrate that a significant improvement in fracture gradient can be achieved with the right clearance between the hole and the casing and the proper sized particles added to the mud system. In addition, the amount of material added has been demonstrated to be as low as two pounds per barrel. With confidence that strengthening can be achieved to the levels of improvement demonstrated, wells can be evaluated with significant cost savings by eliminating casing strings and preserving hole size for completions or further drilling.
This paper assesses the benefits of itabirite (hematite) as a weighting material in heavy oil base systems. A laboratory investigation was conducted to obtain information on a comparative basis between barite and itabirite. Rheological properties and abrasiveness were studied and field results were predicted. As a result of the lab studies, lower field rhe-ology (i.e., PV, YP and Gel Strength) and a slightly more abrasive nature are predicted. Increased penetration rates and improved bit hydraulics are expected. Increased penetration rates and a greater tolerance to drill solids should reduce overall mud cost and well cost. Upon completion of the laboratory study, field tests were made in a development area. Offset information on wells drilled with barite was studied, and variables such as drilling rigs, mud company, solids control equipment, bits, and mud programming were kept as consistent as possible with the exception of itabirite as the mud weighting agent. Results indicate an increase in penetration rates as compared to offset wells, especially in mud weights exceeding 15 lbs/gal. Plastic viscosity was lower as predicted, mud cost slightly decreased, and abrasion did not appear excessive on pump liners and and pump parts. The efficiency of the solids control equipment was increased as shown by the maintenance of a lower percentage of solids in the mud and reduction of the percentage of low gravity solids.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThis paper discusses the design and testing of 10 ¾-in. and 7 5/8-in. casing directional drilling equipment and procedures that ConocoPhillips plans to use on a mature North Sea asset. ConocoPhillips has worked with Tesco Corp. and Schlumberger in assembling the tools necessary to complete this task. These include: downhole casing drilling tools, underreamers, positive displacement motors, MWD tools, rotary steerable systems (RSS), and high capacity winches for this work. Testing this equipment in commercial North Sea operations is prohibitively expensive. Therefore, tests were conducted at a drilling test facility near Cameron, Texas, where operations were conducted over a wide range of rotating speed, weight and flow conditions as well as inclinations from vertical to horizontal. High frequency surface and downhole drilling mechanics measurements assisted in diagnosing problems and improving the systems. The project serves as a blueprint for managing technical developments among multiple operators and service companies.
In January 2007, ConocoPhillips completed what is believed to be the first well directionally drilled with casing using wireline retrievable bottom hole assemblies from an offshore installation. ConocoPhillips has considerable experience with this technology in reducing drilling days on predominately vertical land wells in South Texas. It was desired to determine if the same benefit could be realized in the offshore environment; where directional drilling is required. A candidate development well was identified in Norway on the ConocoPhillips operated Eldfisk Bravo platform that could benefit from advantages seen with Casing while Drilling. Two land based tests were conducted to confirm the ability to conduct casing directional drilling in wells similar to those expected in Norway. Simultaneously, a detailed plan for drilling the well in Norway was developed.Two production casing strings (10 ¾-in. and 7 ¾-in.) were successfully drilled directionally through the overburden section on the Eldfisk well. The well had a complex 3-dimensional well path with inclination up to 60°. All running and retrievals of the BHAs was planned to be done with wireline and a purpose-built traction winch system rated to a working load of 40,000 lbs. Once the 7 ¾-in. production casing was cemented, the casing string was converted to a production liner with an expandable liner hanger and the upper section of 7 ¾-in. was retrieved. In all, 10,968 ft of the 13,600 ft well was directionally drilled with casing.
Managing the disposal of drilling wastes from onshore operations is an escalating concern for the petroleum industry. Many wells are drilled in agricultural areas, posing concerns to the public with respect to disposal methods for drilling wastes. It is critical to appropriately evaluate these wastes to preempt negative environmental impact from improper disposal. The careful selection of drilling fluids and treating chemicals may allow operators flexibility in selecting disposal methods. An attractive option for disposal of onshore drilling wastes is through land treatment or "landfarming". In some cases, environmental quality may be enhanced by the application of wastes that have a positive impact on plant growth. This paper presents the results of a greenhouse plant growth study designed to evaluate the potential for landfarming drilling wastes in agriculturally active areas. Drilling wastes were collected from two wells where a non-halide potassium based product was used to formulate the drilling fluid. The fluid and associated wastes (drill cuttings) were used to conduct replicated growth tests of 2 plant species in 3 geographically different soils at 5 loading concentrations. Plant growth was monitored for over 70 days with intermittent cuttings taken at specific periods. Parameters measured included growth rate, growth index, soil electrical conductivity and exchangeable and leachate potassium in the soils. At the conclusion of the growth period, samples from selected cuttings were dried, digested, and analyzed for metals uptake as compared to the control plants. In addition, non-replicated tests were conducted where germination rates were evaluated at wet waste loadings of up to 50% by volume. Static bioassays were also conducted with two different species using whole mud samples. The results of this study indicate that downhole wastes, when generated with a properly formulated drilling fluid, may be landfarmed and have no adverse effects on growth potential when applied at specific loadings. Introduction Wastes collected during drilling operations consist of the subsurface materials (cuttings) displaced to the surface by the drilling fluid and the drilling fluid adsorbed on the surface of these cuttings. These wastes may be collected and disposed of in a variety of methods, but land treatment or "landfarming" provides the most favorable combination of disposal cost, short and long term liability to the generator, and potential environmental impact. Landfarming is a process in which wastes are incorporated into a soil surface to degrade, transform or immobilize the waste constituents by biological, chemical and physical reactions. Since many wells are drilled in agriculturally active areas, the effect of landfarming on plant growth potential is extremely important. Specific concerns involve (1) the effect of soluble salts and cation mobility on germination and plant growth and (2) heavy metals uptake by the plants that could be passed along the food chain. The advent of polymer based systems and the concern for formation damage of mature domestic oilfields have led to the use of potassium based drilling fluids when penetrating sensitive producing formations. This paper presents the results of a plant growth study in which a non-halide potassium source (potassium sulfate) was used as a drilling fluid additive in an unweighted, low pH, low solids non-dispersed (LSND) mud system. Potassium sulfate was selected because it is commonly used as a fertilizer, particularly for chloride-sensitive crops. P. 163^
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