Lessons Learned from Stimulation of Dibei Tight Gas Reservoir with Strong Heterogeneity in Tarim Basin

Abstract

The Dibei gas field is a naturally fractured tight sandstone gas reservoir in the Tarim Basin, West China. It is characterized by large depth (4600–5200 m), huge thickness (100–200 m), low abundance, low matrix permeability, high pressure (80–95 MPa), high temperature (140 – 150°C) and strong heterogeneity. Different stimulation techniques were applied to improve well production. For the wells with good development of natural fractures, matrix acidizing, acid fracturing or conventional hydraulic fracturing is used. For the wells with low fracture density and huge thickness, separate-layer acid-fracturing, massive separate-layer hybrid fracturing or composite diverting agent is applied to improve stimulation efficiency. The low-damage high-temperature weighted fracturing fluids are used to reduce the effect of reservoir sensitivity and the treatment pressure, and high-strength proppant is used at the same time to keep high fracture conductivity. Meanwhile, large-diameter fracturing string with 3-1/2″ and 4-1/2″ connections is used to decrease pump pressure and increase pump rate. The above technologies were applied in more than twenty treatments in seven wells, of which more than half witnessed production increase. The matrix acidizing or conventional hydraulic fracturing is well performed for the wells with natural fractures, but inefficient for the extremely tight gas wells. In Well A without fractures, the massive separate-layer hybrid fracturing was used. In the treatment, a total of 1,328 m3 fracturing fluid was used, with 50 m3 proppant; the pump rate was 8 m3/min and the maximum pump pressure was 92 MPa. Unfortunately, the post-frac production was not as expected, mainly due to the damage of killing well. In Well B with fractures, high gas production was achieved by acid fracturing, but the gas rate dropped from 258,000 m3 to 51,000 m3 after killing well, and the gas rate never recovered even by acid fracturing, hydraulic fracturing and relieving damage with methanol. The development of natural fractures is the key controlling factor for gas production. Well C, less than 800 m from well B, The development of natural fractures is quite different from Well B, and 98,000 m3 gas rate was acquired after hydraulic fracturing with more than 1,000 m3 low damage high-temperature weighted fracturing fluid and 30 m3 proppant. The development of natural fractures is the key controlling factor for gas production and killing well damage is the fatal blow to the gas production, so the stimulation techniques and working fluid system should be prudently optimized.