Practices of Formation Damage Control for Deep Fractured Tight Gas Reservoir in Western Sichuan Basin

Abstract

AbstractWestern Sichuan deep tight gas reservoir is characteristic of ultra low permeability, natural fractures developed in heterogeneity, partial ultra low water saturation, hard and brittle shale interlayer. The matrix permeability varies between 0.001mD and 0.1 mD, and the natural fracture width is between 10μm and 2.0mm, while the fracture width can reach up to 5.0mm during the well operations. Lost circulation, inducing severe reservoir damage and increasing non-productive time, happens more frequent. The traditional lost circulation control technologies such as physical, chemical or physicochemical methods, used to permanently chock the lost circulation passage of non pay zone, is not applicable to pay zone. One after another technology such as air underbalanced drilling fluids, non-invasive drill-in fluids and the traditional temporary shielding fluids technology(TSF) were executed for prevention of formation damage duo to lost circulation, but they all do not work well. The air underbalanced drilling has to be given up because of formation water influx and wellbore instability, and non-invasive drill-in fluids does not obtain good results duo to low return permeability rate and low loading pressure ability of filtrate cake in the fractured formation. The traditional temporary shielding fluids technology (TSF) is not competent for the damage prevention of the reservoir with ultra narrow pores and throats. In the light of the special geology and engineering characteristics, a named temporary sealing loss (TSL) fluids with inert particles and acid soluble particles are developed to prevent formation damage in leaky fractured reservoirs. Integrating the advantages of non-invasive fluids and temporary shielding fluids, temporary sealing loss (TSL) technology takes advantage of inert bridging particles and acid soluble filling particles to rapidly form tight plugging zone near the wellbore to seal the throats and fractures effectively. After its application, well X2 and X3 obtain gas production of 52.16×104m3/d and 22.37×104m3/d in 2nd member of Xujiahe formation, respectively.