CO2 Foam Fracturing Application in Laminated Shale Oil: Shaping a Green Future of Massive Frac Treatment

Abstract Chang7-3 is a typical laminated shale oil located in the Ordos Basin in northwest China. It is characterized as a deep unconventional reservoir with low porosity, low permeability, and low oil saturation, which makes industrial development extremely difficult. In recent years, to further clarify the exploration potential of such shale oil reservoirs, operators have deployed many wells and adopted massive fracturing treatment with large Stimulated Reservoir Volume (SRV) strategy, but the post-fracturing production is unstable and unsatisfying. The large amount of water consumption induced tremendous pressure on the local ecological environment, which is already dry, rainless, and fragile. The challenge is to find an alternative fracturing technology that could both fully release the potential of Chang7-3 and make a technical foundation for the future green development. In this paper we describe a case study about a trial of applying carbon dioxide (CO2) foam fracturing technology in several horizontal and vertical wells of the Chang7-3 shale oil. By replacing 55 to 65% of water-based fracturing fluid with CO2 while using less proppant, with the help of a foaming agent and the turbulence effect in the treatment string, a uniform CO2 foam fluid can be formed when the critical point of CO2 is exceeded in the reservoir. Although such technology will involve more equipment and higher operational difficulty, the benefits it brings to the operator have achieved the exploration and production goals in the deep shale oil reservoir. With the benefits of several advanced logging tools such as lithology scanning, combinable magnetic resonance, and electrical imaging logging, a tailored CO2 foam fracturing program is proposed with an integrated geology and engineering strategy. More than 60% water consumption reduction is achieved compared to offset wells. A series of valuable engineering insights were gained, such as CO2 foam fluid rheology and working mechanism, operation standard procedure, CO2 foam fluid friction calibration, evolving technical parameters, etc. The post-fracturing production performance is excellent and exceeded the expectations of one well, which achieved the top level of testing production. Oil could be produced during initial flowback, which is rarely seen and has verified the promising features of CO2 foam fracturing technology, such as stronger penetration into the formation leading to high fracture complexity, oil extraction and viscosity reduction effect, flowback enhancement, and less formation damage. This CO2 foam fracturing trial is consistent with the carbon capture, utilization, and storage (CCUS) trend in the oil and gas industry and could help operators accelerate the transformation to green and sustainable development. The technical insights described could be adapted to other blocks with similar reservoir properties to achieve improved post-fracturing production performance.