Research On Gas-liqud Conversion Drilling Fluid Technology Of Gas-Drilling In Xushen Gas Field

As a kind of underbalanced drilling method, gas-drilling can promote drilling and completion schedule greatly. Due to a series of development technology and stratum condition, it is necessary to convert into conventional drilling timely to keep sidewall stable. Once found formation water-out, gas-drilling will be stopped and converted immediately in Xushen gas-field of Daqing. But now, sidewall remains instable in the process of gas-liquid conversion.In view of this problem, fabrics of clay shale samples of gas-drilling section are analyzed firstly and hydration rule is dissected by cuttings roller recovery measuring and expansion rate measuring. While, hydration mechanical property is measured by triaxial-stress apparatus. Then, the mechanism of instability is induced. Owing to poor cementation, illite-rich and Eatmon mixed-layer development locally, mudstone of gas-drilling section is easy to peel off the block after hydration. Combined with micro-cracks, negative pressure difference and the scouring action, it tends to cause wall instability. According to this mechanism and stratigraphic characteristics, the performance requirements of gas-liquid conversion mud are cleared. Establishment of plugging ability evaluation is based on particle size distribution analysis and the micro-cracks plugging experiments. Through optimizing various treatment agents, available organic-silicon mud can be improved and the final formula is given, which enhances its inhibition, ability of filtration control, wettability reversal and plugging of the formation to form the gas-liquid conversion drilling suitable to realize "gas" and "fluid" conversion and join smoothly.