Fracture-network acid fracturing technology for ultra-high temperature fractured metamorphic gneiss condensate reservoirs: A case study of the Archean buried-hill reservoirs of the offshore A Gas Field

Abstract

In order to solve the problems caused by restricted application of offshore hydraulic sand fracturing measures, limited stimulation potential of gneiss matrix acidizing and sand control completion mode, this paper systematically studies the geological and engineering feasibility of fracture-network acid fracturing and analyzes the difficulties and challenges in acid fracturing stimulation based on the characteristics of offshore large-scale monoblock Archean buried hill gneiss condensate reservoir A in terms of great burial depth, ultra-high temperature, abnormal pressure, ultra-high condensate content, small difference between formation pressure and dew point pressure, strong reservoir heterogeneity and complex lithology. Then, the realization way of acid fracturing with complex fracture networks is put forward. Finally, gas-wetting reversal agent, through-screen liquid temporary plugging agent and fracture-network acid system with low damage are developed. And the following research results are obtained. First, nano gas-wetting reversal agent collaborating with multi-hydrogen chelating acid can realize effective etching to form high-conductivity fracture networks and change rock wettability, so as to improve the relative permeability of gas phase. Second, liquid temporary plugging agent can achieve a temporary plugging and self-cleaning effect by means of phase transformation and can smoothly run through sand control completion tools, such as screen pipe. Third, based on the optimized design of process parameters, the fracture-network acid fracturing technology is practically applied to Well H1 in offshore condensate reservoir A. The injected liquid volume is totally 489.8 m3. After the application of the measure, the single-well gas production rate is 48% higher than the initial value and the condensate production rate is 11% higher, indicating a remarkable application effect. In conclusion, the developed liquid temporary plugging agent realizes temporary plugging and diversion, and the acid system and process parameters for the fracture-network acid fracturing of gneiss are optimized, which provides an effective technical support for the efficient development of offshore ultra-high temperature fractured gneiss condensate reservoirs and the reference for the stimulation of similar oil and gas reservoirs in the other areas.