Research on reservoir drill-in and completion fluid with unique direct backflow property for gravel-packed openhole construction

Traditional completion fluids used in construction of gravel-packed openhole in offshore oil and gas fields have been suffering from problems of complicated completion operation and risks of secondary formation damage. In this work, a new reservoir drill-in and completion fluid has been designed with unique direct flowback capability, in order to simplify process of well construction and highly reduce potential reservoir damage. An improved temporary plugging strategy was firstly analyzed, wherein the D90 embedding rule and low shear rate viscosity (LSRV) law that contribute significantly to the unique direct backflow property were systematically elucidated, in combination to reservoir features of oil fields in South China Sea. To realize the one-way seal on the reservoir surface, the size of embedding particles was controlled in the range of 2.7–6.7 μm, and LSRV was optimized around 30,000 mPa s. Furthermore, the reservoir drill-in and completion fluid was experimentally prepared and evaluated, and diverse application properties such as rheology, filtration, anti-contamination, inhibition, and reservoir protection were achieved in terms of standards of wellbore working fluids and trial requirements. Finally, field trial validated the applicability of reservoir drill-in and completion fluid in constructing gravel-packed openhole in offshore oil and gas fields, and the period of openhole completion reduced by about 9 h relative to that of the traditional acidizing operation.