TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractMitigating drilling hazards-balancing drilling risks against the optimum well design while preparing for unplanned drilling events-has been a challenge to cost-effective well construction for decades. The pore pressure/formation fracture gradient balancing challenges mixed with the unexpected encounters with shallow flows, unstable formations, overpressure formations and depleted formations makes AFE (authorization for expenditures) goals dim.Excessive use of loss circulation pills and traditional contingency liners drive well costs up and jeopardize reaching total depth (TD) with an effective completion. A drilling hazard remediation solution could be as simple as using that planned contingency liner or using drill-in casing to fight sloughing formations. However, the use of conventional solid expandable drilling liners can drive excessive risks into the well and even cause a costly sidetracking of the well.Operators in the Gulf of Mexico, the North Sea and in Asia Pacific have been successfully using a set of proven well construction tools with a more "Fit for Purpose" application to mitigate drilling problems that have resulted in excessive nonproductive time (NPT) during drilling operations. These systems are used only when necessary to mitigate the well challenge, allowing the well construction to continue while minimizing their NPT fighting these well problems.This paper describes some of these "fit for problem" well construction tools and their applications in recent case histories.
Cost overruns can easily manifest during well construction due to unexpected issues including lost returns, differential sticking, and narrow pore pressure/fracture gradients. To better plan for potential overruns, operators sometimes earmark 10 to 25% of the Authorization for Expenditures (AFE) to cover the unexpected, which can significantly impact drilling budgets. Technical and operational risks versus the potential return on investment (ROI) are critical factors in determining whether a project proceeds. Too often the best drilling practices used to address trouble zones are limited to a few conventional methods with a narrow range of effectiveness. Also, a lack of rock mechanics knowledge can prevent the most efficient solution being applied. Some operators are implementing planning programs that assess and integrate the latest processes and technologies to address drilling risks up-front. Cutting-edge technologies such as managed pressure drilling methods, drilling with casing / drilling with liners, and solid expandable casing have been highly effective. Implementing proactive evaluation processes and applying the latest tools and techniques can efficiently address operational risks and trouble zones to ultimately reduce NPT and associated costs. Employing common practices and technologies that are typically ineffective and that drive up NPT cost should be considered unacceptable. Common sense well construction evaluation processes used in conjunction with validated conventional and new technologies have proven their worth by reducing expenditures and risks, preventing the loss of wells, and increasing the operator's ROI. This paper will review real drilling challenges that have been encountered and the common practices that were employed to address these drilling hazards. This paper will compare and contrast how these same circumstances have and can be addressed much more efficiently with engineering evaluation processes that help determine the best drilling tool and/or technique to mitigate risks and reduce NPT.
Cost overruns can easily manifest during well construction due to unexpected issues including lost returns, differential sticking, and narrow pore pressure/fracture gradients. To better plan for potential overruns, operators sometimes earmark 10 to 25% of the Authorization for Expenditures (AFE) to cover the unexpected, which can significantly impact drilling budgets. Technical and operational risks versus the potential return on investment (ROI) are critical factors in determining whether a project proceeds.Too often the best drilling practices used to address trouble zones are limited to a few conventional methods with a narrow range of effectiveness. Also, a lack of rock mechanics knowledge can prevent the most efficient solution being applied.Some operators are implementing planning programs that assess and integrate the latest processes and technologies to address drilling risks up-front. Cutting-edge technologies such as managed pressure drilling methods, drilling with casing / drilling with liners, and solid expandable casing have been highly effective. Implementing proactive evaluation processes and applying the latest tools and techniques can efficiently address operational risks and trouble zones to ultimately reduce NPT and associated costs.Employing common practices and technologies that are typically ineffective and that drive up NPT cost should be considered unacceptable. Common sense well construction evaluation processes used in conjunction with validated conventional and new technologies have proven their worth by reducing expenditures and risks, preventing the loss of wells, and increasing the operator's ROI. This paper will review real drilling challenges that have been encountered and the common practices that were employed to address these drilling hazards. This paper will compare and contrast how these same circumstances have and can be addressed much more efficiently with engineering evaluation processes that help determine the best drilling tool and/or technique to mitigate risks and reduce NPT.
The gas fields of the western Piceance basin in northwestern Colorado present significant challenges to drilling and casing operations. This area has complex geology, with dipping formation beds that lead to "crooked hole" drilling. Fractured formations cause problems, including lost circulation while drilling, and failure to return cement to surface during primary cement jobs of the 9 5/8-in. casing. Sometimes casing cannot be run to total drilled depth. After review of the problems, an operator in the region concluded that a different approach was warranted and selected drilling with casing (DwC) as an alternative to investigate. DwC, combined with stage cementing of the surface casing, was expected to yield a significantly more effective surface-hole drilling and casing operation, reducing nonproductive time (NPT) and the associated cost. This paper reviews the problems encountered in conventional surface-hole drilling and casing running operations in the Piceance basin. It also reviews the operator's decisions for a DwC approach. A case history of a DwC-with-stage-tool cementing operation and its successful conclusion is presented. Background The operator has been drilling in the gas fields of the Piceance basin since 2003. Figure 1 shows a general map of the area. The operator has experienced difficulty drilling and casing the surface hole, which is typically targeted to approximately 3,100 ft measured depth (MD). Problems are caused by dipping formation beds, rock stresses, and lost-circulation intervals. Conventional drilling practices use mud motors and low weight on bit (WOB) to drill a 12 1/4-in. surface hole because high WOB with conventional drilling assemblies often results in severe inclination increases, sometimes in excess of 7°. Table 1 shows a typical conventional bottom hole assembly (BHA) previously used to drill surface hole in this area. Table 2 shows maximum hole inclinations measured in the surface holes drilled with both conventional BHAs and DwC. The surface-hole geology predominantly consists of sandstone, siltstone, and limestone stringers with interbedded shales. Figure 2 shows a typical mud log section of the surface interval. The naturally fractured formations often lead to lost-circulation problems. With insufficient volumes of drilling fluid being circulated, sloughing shales and subsequent pack-off and sticking situations result. After drilling, the hole conditions encountered make running the 9 5/8-in. surface casing to the planned depth problematic, even when the casing is washed down. Many times, as seen in the conventionally drilled holes, the operator has not been able to get the 9 5/8-in. casing to its planned setting depth. On two of the conventionally drilled wells, the casing was set 300 ft and 427 ft short of total depth (TD). Unplanned hole conditioning trips have often resulted in NPT and, in the worst cases, fishing operations have been required because increased open-hole exposure time has led to stuck pipe. NPT was as much as 15 days in the worst case. The hole conditions also often have led to poor-quality primary cement jobs and problems in satisfying the requirements of the local regulatory authority, the Bureau of Land Management (BLM). Failure to circulate cement to surface resulted in the requirement to run a cement bond log (CBL) to evaluate the integrity of the cement job which, in turn, often led to the need for remedial cementing and wireline operations to reach an acceptable quality of cementation. This remedial work often has resulted in 3 to 4 days of NPT. Table 3 shows NPT as a result of drilling problems, casing running problems, and cementing issues before and during implementation of DwC technology. Evaluation of DwC With knowledge of surface-hole difficulties, the operator began to investigate alternative solutions to fulfill the following objectives:
Cost overruns can easily manifest during well construction because of unexpected issues including lost returns, differential sticking, and narrow pore pressure/fracture gradients. To better plan for potential overruns, operators sometimes earmark 10 to 25% of the Authorization for Expenditures (AFE) to cover the unexpected costs, which can significantly affect drilling budgets. Technical and operational risks versus the potential return on investment (ROI) are critical factors in determining whether a project will proceed. Too often the best drilling practices used to address trouble zones are limited to a few conventional methods with a narrow range of effectiveness. Also, a lack of rock mechanics knowledge can prevent the most efficient solution being applied. Some operators are implementing planning programs that assess and integrate the latest processes and technologies to address drilling risks up-front. Cutting-edge technologies such as managed pressure drilling methods, drilling with casing, drilling with liners, and solid expandable casing have been highly effective. Implementing proactive evaluation processes and applying the latest tools and techniques can efficiently address operational risks and trouble zones to ultimately reduce nonproductive time (NPT) and associated costs. Employing common practices and technologies that are typically ineffective and that drive up NPT cost should be considered unacceptable. Common-sense, well-construction evaluation processes that are used with validated conventional and new technologies have proven their worth by reducing expenditures and risks—preventing the loss of wells and increasing the operator’s ROI. This paper reviews real drilling challenges that have been encountered and the common practices that were employed to address these drilling hazards. Also this paper compares and contrasts how these same circumstances have and can be addressed much more efficiently with engineering evaluation processes that help determine the best drilling tool and/or technique to mitigate risks and reduce NPT.
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