Coring Techniques in Shale Formations and Their Field Application

During coring in shale formations, the ROP (rate of penetration) is normally low, and core breakage, plugging and sticking occur frequently and the core recovery rate is low. In addition, they tend to fracture at bedding planes when being taken out of the core barrels. Therefore, the subsequent core analysis is impacted adversely. In order to deal with these difficulties, the original steel inner core barrels were replaced with high-strength low-friction aluminum alloy ones, and core lifting and transferring tools were transferred to the surface. New wear-proof and impact-resistant coring bits were developed too. A model was built to analyze the stability of coring tools. Finally, coring tool assembly and parameters were optimized on the basis of theoretical calculation results. When all these techniques were applied comprehensively on well site, ROP increased by 100%, single-barrel footage increased by 50%, core handling time reduced to 20-30 minutes, and the core recovery rate of typical blocks achieved over 95%. It indicated that new coring techniques can meet the requirements of coring in shale formations and considerably improve coring efficiency and recovery rate.