ABSTRACT:
In one of the major ultra-high temperature and ultra-deep reserve in West China, hydraulic stimulation confronts challenges of true vertical depth more than 8,600 m and bottom hole temperature beyond 180°C. The long injection path from surface to stimulated formation induces significant friction which leads to very high surface pressure, pushing the limit of surface pumping equipment. In addition, the ultra-high temperature disqualifies any conventional fluid system due to failure of maintaining desirable properties under high temperature. As counter measures the authors explored and researched in a novel fluid system with high specific gravity and high temperature resistance tailored for this reserve. In lab, the fluid systems is systematically evaluated in its temperature and shear resistance, friction reduction, gel breaking property and core damage rate and the residue content. The formula of fracturing fluid is 0.5 wt% polymer GX-100 + 0.65 wt% cross-linker WQ-180 + 2.5 wt% pH regulator+weighting agent KCl. Results show that the fluid system has excellent temperature and shear resistance, and capable of achieving density up to 1.30 g/cm3. Under 180°C, 170 s-1 condition, the shear viscosity of the fracturing fluid remains over 50 mPa•s, with friction reduction above 75% for as long as 90 mins continuous shearing and the advantage of low residue, complete gel-breaking and low formation damage. The novel fluid system is a fit-for-purpose solution to the problem of ultra-deep and ultra-high temperature reserve hydraulic stimulation and hence improving the stimulation success rate.
1. INTRODUCTION
Hydraulic stimulation has been widely used in oilfields to increase the production of hydrocarbons from subterranean reservoirs, especially unconventional reservoirs. Without hydraulic stimulation, most unconventional wells would not be economica (Song et al., 2016). Shunbei block, the midwestern part of the northern depression of Tarim basin, is located in Shaya county, Xinjiang, China. Fracturing must be applied to realize commercial production for tight reservoir. However, conventional fracturing fluid can neither satisfy the requirement of high temperature, nor effectively reduce the friction while treating, resulting in excessively high surface pressure, representing a high operational risk. Therefore, it is necessary to carry out research on unconventional fracturing fluid technology and formulate a fluid system suitable for the ultra-deep and ultra-high temperature reservoirs.
