Wireline Microfracturing: Ultrahigh-Value Stress Measurements at Ultrahigh Pressures in an Ultradeep Lower Tertiary Play

摘要

The measurement of geomechanical properties of reservoir rock and caprock for completion optimization,rnenhanced oil recovery (EOR), and disposal/storage of any kind is becoming an integral and key aspect ofrnasset evaluation and appraisal. One of the most important of these characteristics is an in-situ evaluationrnof the magnitude and variation of the minimum in-situ stress, the measurement of which is critical forrngeomechanical modelling and thereby a range of applications such as well construction, caprock integrity,rnand completion optimization.rnA wireline formation testing (WFT) tool is a common approach for obtaining direct measurements ofrnthese stresses at a range of depths. This process is referred to as microfracturing and is most typicallyrnperformed in an openhole environment. Typical toolstrings consist of a straddle packer arrangement, arnpumping mechanism, gamma ray for accurate depth correlation, a motorized valve/manifold arrangement,rnand pressure/temperature gauges. To perform a stress test, a specific interval of the wellbore is isolatedrnby inflating the straddle packers. The interval is then pressurized by incrementally pumping fluid until arntensile fracture has been initiated. In an open hole, the fracture will initiate and propagate normal to thernminimum stress at the wellbore and multiple injection and falloff cycles are subsequently performed tornensure fracture growth beyond the influence of the hoop stress regime. The data are then analysed torndetermine fracture initiation, reopening, propagation and closure pressures. Additionally, it may bernpossible to approximate fracture orientation, if an image log is available.rnThis paper describes the process of obtaining minimum in-situ stress measurements using a WFT andrnadvanced integrated stress analysis (ISA) process, in an ultradeep reservoir at ultrahigh pressures. Lessonsrnlearned and best practices are highlighted along with their importance for efficient job execution. Thernintegrated geomechanical analysis covers subsequent generation of a calibrated stress model withrnminimum horizontal stress measured during microfracturing. Factors include evaluation of the stressrncontrast in the target formations and evaluation of the overburden gradient and mechanics for microfracturingrnjob design for future operations (breakdown pressure) and lessons learned such as station selection,rnbackup packer availability, and influence of stress cage material on breakdown, to name but a few.rnObtaining accurate knowledge of in-situ minimum stress values, based on actual measurements, is arnkey step on the road to effective execution, and the earlier that this is achieved, the more efficient the results of any development. This paper summarises the successful application of the WFT approach inrndelivering such data under extremely harsh depth and pressure conditions, but resulting in a measurementrnfrom which numerous subdisciplines can conduct their decision making and design.