In recent years there has been a growing awareness of the importance of Wellbore Strengthening Material (WSM) for sealing drilling-induced and natural fractures both in permeable and impermeable zones. This paper details the application of a software tool designed specifically for determining the optimum blend of WSM to drill the formations of the challenging Cashiriari field in Peru.Several theories have been proposed to explain techniques which are in vogue for mechanically strengthening wellbores so as to control fracture propagation: Hoop Stress Enhancement ("Stress Cage") theory involves increasing the near-wellbore stress, which is usually carried out by opening fractures to tighten the wellbore and sealing the fractures immediately in that open state; "Fracture Closure Stress" theory utilizes high-fluid-loss materials to plug and tighten existing fractures; and "Fracture Propagation Resistance" theory involves isolation of the fracture tip. The design and successful utilization of a blend of WSM based on the opening and sealing of fractures suggests that these three theories are, in many respects, complementary.Any theory explaining a particular problem is ultimately judged by its practical application. Cashiriari field, known for expected mud losses to both natural and drilling-induced fractures in primarily permeable formations, is where this wellbore strengthening application took place. The optimum blend of particulates, designed using wellbore-strengthening (WBS) software, was applied consistently on the wells drilled by the operator in the Cashiriari field in the 2009-2010 campaign. Fracture resistance was increased up to 0.8 lb/gal above the minimum horizontal stress for drilling and up to 1.68 lb/gal for running casing and cementing operations. Specialized logs showing the presence of WSM inside fractures were an important tool for optimization of the WSM blend.WSM design software takes in account a multitude of drilling parameters and rock properties to predict the fracture width and estimate the required size distribution and concentration of the WSM particulates. Consequently, the WBS solution reduced lost circulation as a primary contributor of costly and time-consuming lost circulation incidents in the Cashiriari field. Further, it is anticipated that as the WBS approach is applied more widely, the incidence of lost circulation events will be greatly reduced.
Objectives/Scope A major Operator in Kuwait have used historically Non-Aqueous Fluid (NAF) to drill the buildup section through the challenging shale formations, mainly due to wellbore stability issues and lubricity requirements. As part of the operator's environmental improvement strategy, the operator and fluids provider team identified potentially fit for purpose High Performance Water Base Mud (HPWBM) as the most suitable, environmentally acceptable alternative to NAF’s. Methods, Procedures, Process A HPWBM system was designed and proposed based on extensive laboratory testing to overcome drilling challenges. Inhibition characteristics and formation sealing capabilities of conventional KCL polymer mud with sulphonated asphalt were enhanced by using a liquid polyamine based clay hydration suppressant and a co-polymeric nano-sized shale-sealing additive. A customized bridging package based on the pore size distribution was also introduced, using calcium carbonate and resilient graphite particles. The combination of effective bridging and sealing polymer helped in sustaining high overbalance to avoid differential sticking tendency, designed in laboratory conditions during the planning stage. Results, Observations, Conclusions The field trial was a great success compared to the use of conventional fluid systems and methodologies. Using High Performance Water Base Mud, the operator successfully drilled and cased 12.25" and 8.5" sections as per plan with stable wellbore indicated by the smooth trips and no string stalling or sticking tendency. Drilled 1077 feet of 12.25-in hole section crossing Ahmadi shale and 683 ft. of 8.5" section crossing troublesome Wara shale without any well-bore instability issues even at high inclination. Also, while drilling across depleted Mauddud limestone with 1800-psi overbalance, no differential sticking tendency observed. Both sections were completed in record 11 days, fastest comparing to offset wells drilled with NAF. Novel/Additive Information In this paper, the authors will detail this novel approach of using an environmentally acceptable HPWBM system in the North Kuwait Basin, from planning to execution, which can be implemented further on the field and offers significant cost saving and reduces the risk of HSE issues related to Diesel based NAF systems.
Drilling for hydrocarbons in the extreme reservoir pressure and temperature remains one of the most challenging operation, especially related to drilling fluids. A combination of excellent teamwork and fluids technology proved to be the recipe for successfully drilling in these extreme conditions for TotalEnergies shale-gas play, onshore Abu-Dhabi, United Arab Emirates. The success on drilling deep (6,200mMD), long lateral displacement (2,000m) wells with an integrated global operator is a balance, dependent on frequent and transparent communication between the team members, of excellence in well planning, extensive laboratory testing, procurement and supply of resources, flawless field execution, and a diligent post-well review with the operator. More commendable is this success was achieved while dealing with operational challenges amplified by the pandemic restrictions on personnel and materials movement. The design of the environmentally and economically acceptable aqueous fluid met stringent fluid design criteria, wellbore and temperature stability for drilling and data acquisition performance goals. The high-density HT drilling fluid is designed to have the minimum amount of solids by using a Sodium Chloride combined with a Sodium Bromide brine, weighted up with ultra-fine grind barite. Viscosity and fluid-loss are controlled with a unique additive, a dual-function, branched synthetic polymer. The environmentally acceptable aqueous drilling fluid delivered a barite sag-free operation in these highly deviated wellbores, delivering a balance between a low-equivalent circulating density and excellent hole cleaning, compatibility with the reservoir formation, and long-term stability to enable logging with no formation closure in a deep, high temperature drilling environment. Additional achievements of the fluid were the low HPHT filtration, good lubricity for increased rate of penetration, and reusability on the subsequent wells thus improving the sustainability profile by reducing disposal. Successful coring and extended wire logging the reservoir section was an excellent test for this fluid. The balance between a brine base, filtrate-loss, and viscosity-increase additive for fluid design, coupled with excellent field engineering provides the long-term thermal stability of a drilling fluid able to tackle drilling a reservoir reaching a depth past 6 kilometers.
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