EXPERIMENTAL STUDY ON THE CHARACTERISTICS OF A NOVEL SELF-DEGRADABLE PLUGGING AGENT USING FOR WATER-BASED DRILLING FLUIDS

摘要

The Dongsheng gas field in the Ordos Basin is one ofthe major natural gas reserves in China. Dur-ing drilling, the drilling fluid can easily leak into the fractured reservoir and cause damage, which se-verely restricts the efficient drilling and development of fractured reservoirs. Reservoir fractures are not only a channel for the loss of drilling fluid to con-taminate the reservoir, but also a channel for oil and gas seepage. In the process of drilling a fractured res-ervoir, it is necessary not only to seal the fractures of the reservoir under pressure, but also to remove the plugging after completion to protect the reservoir and reduce the cost of completion operations. There-fore, since common temporary plugging materials cannot be self-degradable, the self-degradable plug-ging particles and fiber materials have been devel-oped. With the help of thermogravimetric test, compressive strength experiment, Fourier infrared spectrometer, scanning electron microscope, reser-voir protection experiment and crack plugging ex-periments, etc., we discuss the main influencing fac-tors of the degradation performance of the new self degradable plugging agent,optimize the self-de-gradable drilling fluid system, and reveal the mech-anism of self-degradation.Experiments show that the newly developed self-degradable plugging parti-cles have high compressive strength (breakage rate <5).Their degradation rate increases as the tem-peraturerises and can be selfdegradable in oil or wa-ter-based drilling fluids. The optimized self-degrada-ble drilling fluid system formula has good rheology and fluid loss performance. The core permeability recovery value after self-plugging is more than 85. The plug pressure bearing capacity can reach 8.0MPa, and the sealing layer realizes self-degrada-tion after 72 hours in high temperature water envi-ronment, with the breakthrough pressure of only 0.5. 1.0MPa.It isexpected that thenewly developed self-degradable plugging particles can solve the engi-neering technical problems in the Dongsheng Gas Ficld.