Formation damage control of saline-lacustrine fractured tight oil reservoir during well drilling

Abstract

Formation damage is commonly known as a great cause for the production decline, owing to the unclear formation damage mechanisms under the reservoir geological and engineering conditions. This paper aims to develop a formation damage control technology during drilling for the protection of the natural productivity of saline-lacustrine reservoir. Reservoir geological characterization is first presented, including formation mineralogy, petrophysical properties, and fracture developing features. Fluid and stress sensitivity and in situ drilling fluid damage are experimentally evaluated under the simulated reservoir conditions. Successively, formation damage mechanisms during drilling are comprehensively summarized based on the evaluation results. It is believed that lost circulation is the main reason for formation damage, which further induce other damage. Given the formation damage mechanisms, principles of formation damage control technology for saline-lacustrine carbonate reservoir are explored, and in situ drilling fluids are optimized. The optimized drilling fluids are validated by lab experiments and field trials in Qaidam Basin. Field trials indicate that daily decline rate of productivity is decreased and per-well daily yield is increased by 7.7% year-on-year by using the optimized drilling fluids. This work could provide an effective guideline of formation damage control for saline-lacustrine reservoirs.