Abstract
Oil-based drilling fluids (OBDFs) have a strong wellbore stabilization effect, but little attention has been paid to the formation damage caused by oil-based drilling fluids based on traditional knowledge, which is a problem that must be solved prior to the application of oil-based drilling fluid. For ultradeep fractured tight sandstone gas reservoirs, the reservoir damage caused by oil-based drilling fluids is worthy of additional research. In this paper, the potential damage factors of oil-based drilling fluids and fractured tight sandstone formations are analyzed theoretically and experimentally. The damage mechanism of oil-based drilling fluids for fractured tight sandstone gas reservoirs is analyzed based on the characteristics of multiphase fluids in seepage channels, the physical and chemical changes of rocks, and the rheological stability of oil-based drilling fluids. Based on the damage mechanism of oil-based drilling fluids, the key problems that must be solved during the damage control of oil-based drilling fluids are analyzed, a detailed description of formation damage characteristics is made, and how to accurately and rapidly form plugging zones is addressed. This research on damage control can provide a reference for solving the damage problems caused by oil-based drilling fluids in fractured tight sandstone gas reservoirs.
Highlights
Fractured tight sandstone formations have special engineering geological characteristics and are vulnerable to damage caused by the invasion of foreign fluids during drilling and completion
Oil-based drilling fluids (OBDFs) is more stable than water-based drilling fluids (WBDFs), and OBDF has been widely used in fractured tight sandstone formation drilling as the cost of OBDF has approached that of WBDF in recent years [1]
WBDF theories and methods rarely take into account the causes of different types or degrees of damage caused by different fluids, they objectively form a thorough understanding of the reservoir protection effects of OBDF
Summary
Fractured tight sandstone formations have special engineering geological characteristics and are vulnerable to damage caused by the invasion of foreign fluids during drilling and completion. The research on formation damage caused by OBDF has mainly focused on solid phase invasions, wettability changes, and oil traps and there are relatively few studies on why OBDF causes these damages. The change in properties of fractured tight sandstone in an OBDF environment is one of the key factors causing damage to reservoirs. WBDF theories and methods rarely take into account the causes of different types or degrees of damage caused by different fluids, they objectively form a thorough understanding of the reservoir protection effects of OBDF. The damage causes of OBDF to the fractured tight sandstone reservoir in the Keshen Block of Tarim Oilfield, China, are studied through three aspects: the multiphase fluid characteristics of the seepage channel, the changes in the petrophysical and chemical properties, and the rheological stability of OBDF. Based on the study of the formation damage of OBDF, correcting the prejudice of low damage of OBDF over a long period of time is one of the important measures used to effectively improve the efficiency of oil and gas exploitation and to realize the efficient development of oil and gas fields
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