Development and Field Application of a Novel Ultra-High Temperature Seawater-Based Fracturing Fluid System for Deep Offshore Reservoirs

Abstract

Deep offshore hydrocarbon reservoirs are commonly characterized by ultra-high bottomhole temperatures exceeding 180°C and severe freshwater shortages, posing substantial technical challenges to conventional hydraulic fracturing operations. Traditional freshwater-based fracturing fluids fail to adapt to high-temperature and high salinity marine environments and are susceptible to thermal degradation, premature crosslinking, and inadequate proppant transport capacity. Meanwhile, offshore freshwater desalination and transportation significantly increase operational costs and construction risks. To address these critical engineering challenges, this paper develops a novel ultra-high temperature seawater-based fracturing fluid system tailored for deep offshore reservoir stimulation. A salt tolerant thickener is optimized and paired with a delayed organometallic crosslinker to effectively mitigate interference from high salinity ions and divalent cations in raw seawater, eliminating the dependence on freshwater supplies and complex desalination facilities. A comprehensive series of high-temperature high-pressure (HTHP) rheological tests, proppant transport simulations, gel breaking performance evaluations, and core damage experiments are conducted to systematically validate the overall performance of the fluid system. Laboratory results demonstrate that the optimized seawater-based fracturing fluid maintains a dynamic viscosity above 300 mPa·s after 120 minutes of continuous shearing at 180°C and exhibits superior thermal stability at 200°C without degradation. The fluid delivers stable proppant suspension performance and controllable gel breaking characteristics, with a core permeability damage ratio below 15%, substantially outperforming conventional freshwater-based fracturing fluid systems. Building on laboratory validation, full scale field trial is performed in a well with a bottomhole static temperature of 190°C. Raw seawater is directly blended with fluid additives via real-time on-the-fly mixing during pumping operations. Field results reveal stable treating pressure throughout the entire fracturing operation, enabling efficient proppant placement without screen-out, salt precipitation, or equipment scaling issues. Post-fracturing production data indicate that the productivity of the treated well is 25% higher than that of adjacent wells stimulated with conventional freshwater-based fracturing fluids. As deepwater oil and gas exploitation gradually extends to deeper strata and harsher marine environments worldwide, the contradiction between limited on-site freshwater resources and large volume fracturing fluid consumption has become increasingly prominent. Conventional water resource allocation modes can no longer match the large scale, continuous and low carbon development requirements of modern offshore oilfields. This study presents the first successful field application of raw seawater-based fracturing fluid under 190°C ultra-high temperature offshore conditions, filling the technical gap for high temperature seawater fracturing in deep offshore reservoirs. The proposed fluid system and chemical formulation framework can completely replace freshwater for ultra-high temperature fracturing operations, considerably reducing freshwater transportation and desalination costs while ensuring reliable fracture conductivity and construction safety under extreme thermal conditions. This paper provides a sustainable and cost-effective technical solution for the efficient development of global ultra-deep high temperature hydrocarbon reservoirs and offers a reference for the research and development of environment-friendly working fluids for marine engineering.