Factory Drilling and Fracturing Technology for Tight Sandy Conglomerate Oil Reservoir in the Junggar Basin

Abstract

The Triassic Baikouquan Formation reservoir in the Mahu Sag, Junggar Basin is characterized by tight sandy conglomerate oil reservoir with long drilling cycle and great fracturing difficulty. The factory drilling and fracturing techniques of horizontal wells for the Ma131 Well Block of Mahu Oilfield have been determined by regional geological characteristics research and optimization scheme design. The key technologies for horizontal well drilling speed improvement were explored by designing small three-stage wellbore structure, customizing the PDC bit properly, optimizing drilling tool combination, and selecting the drilling fluid with inhibition and plugging ability. The factory reservoir stimulation technique carried out horizontal well hydraulic fracturing with small well spacing for two sets of beds, and adopted bridge plug + clustering perforation staged fracturing and slick water + gel composite fracturing technology. 12 wells in a drilling pad were arranged in the demonstration area with the depth of 5000m, the distance between adjacent sections was 150m or 100m, with the horizontal section length of 1800m. Batching drilling operation pattern was adopted, with 3⁃well drilling for each of rig. Rapid inclining prevention drilling through vertical sections adopted PDC bit + screw + MWD, with high rotary speed and high flow rate. In the build-up section, radical drilling parameters was used to improve the top drive rotary speed and release the torque. In the horizontal sections, rotary steering tool + low speed high torque screw was adopted. The application of this technology achieved good results, with average drilling cycle of 48.3 d and average ROP of horizontal section increased by 77%. The fracturing construction adopted high pad fluid ratio, high sand ratio and high pump rate. More than 10,000 m3 fluid was injected in a single well with high-intensity proppant injection. The factory operation was carried out in the order of construction from the two sides to the middle well with microseismic monitoring. Factory fracturing with small well spacing generated stress interference and improved the fracture reconstruction effect. Higher shut-in pressure, more microseismic events and large-scale stimulated reservoir volume had been carried out in horizontal wells fractured later. The factory drilling and fracturing techniques of horizontal wells for the Ma131 Well Block have achieved the goals of improving drilling speed and volume fracturing, which provided technical support for the efficient development of the tight sandy conglomerate oil reservoir of the Mahu Oilfield.