Horizontal Well Technology for Tight Reservoirs with Coal Seams in the Fangzheng Fault Depression

Abstract

In the Fangzheng Fault Depression Cretaceous reservoirs represent significant resources that are deeply buried, have very low porosity and permeability, and low rates of production at single wells when using conventional technology. Their conditions do allow increased production via horizontal wells. The top of Cretaceous tight reservoirs are adjacent to coal seams and therefore have a high risk of fracturing when drilling is taking place. At present, there is relatively little experience, either at home or abroad, for the exploration of coal seams immediately above horizontal sections. For the first time, horizontal wells have been implemented in the Fangzheng Fault Depression, something that represents a significant technological challenge. This practice draws on the horizontal well design, drilling and tracking, and large-scale volume-fracturing technology, using a technique known as “three optimizations, two accuracies, and one match,” in the Daqing Oilfield (Cui et al. in Pet Geol Oilfield Dev Daqing 33(5):16–22, [1]). Starting with selective lateral drilling and the determination of horizontal well orientation, fine seismic lateral predictions of coal seams and target layers were carried out. During the drilling process, integrated drilling, cutting logging, and logging while drilling, quickly allowed the identification of coal seams. An effective horizontal well technology, that prevents and controls coal wellbore stability, was formulated. Drilling-adjustment techniques were used to ensure the drilling trajectory deviations required due to variations in formation dip angle. To increase oil well productivity and reduce perforation, open hole stage fracturing technology was adopted. Output from a horizontal well was found to be 16 times greater than from a single well—the effect of this on increased production cannot be overstated. During this investigation valuable experience was accumulated in horizontal well drilling and fracturing of tight reservoirs with coal seams in fault basins.

Copyright 2018, Shaanxi Petroleum Society.

This paper was prepared for presentation at the 2018 International Field Exploration & Development Conference in Xi’an, China, 18–20 September 2018.

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