Sensitivity Analysis and Optimization of Technological Parameters During Coupled Liquid CO2 Fracturing-Huff and Puff Treatment in Tight Oil Reservoirs

Abstract

Tight oil reservoirs are currently a primary focus of exploration and development activity all over the world. Fracturing treatment and water/gas flooding are two effective ways to boost recovery. As no water phase present, CO₂ is often used as treatment fluid in both stimulation and EOR operations, which has provided not only an excellent opportunity to improve oil recovery, but also a chance to sequester CO₂ to reduce environment footprint.

Coupled liquid CO₂ fracturing–huff and puff treatment is combination of CO₂ stimulation and CO₂ EOR, aiming to maximize the productivity of tight oil reservoirs. The major difference lies in soaking time after CO₂ injection completed, which is not incorporated in conventional fracturing operation. In this work, we develop an analytical procedure and methods for analyzing technological parameters during coupled liquid CO₂ fracturing –huff and puff treatment. Several parameters, such as fracture length, fracture conductivity, fracture spacing, CO₂ injection volume, soaking time, bottom hole flowing pressure (BHFP) are studied. Compositional numerical model is employed to simulate the flow process and interaction of CO₂ and oil in reservoir. The cubic Peng-Robinson equation of state is used for phase behavior calculations. Orthogonal analysis method is then utilized to analyze the sensitivity of technological parameters and optimization is implemented accordingly.

The results show that the production rate of coupled liquid CO₂ fracturing –huff and puff treatment is better than both CO₂ fracturing treatment and CO₂ huff and puff treatment. From the perspective of cumulative recoverable reserves, it is found that BHFP is the most important parameter, while soaking time has minimal impact. With the increasing of the BHFP, cumulative recoverable reserve is declining. With the extension of soaking time, the production rate is increasing at the beginning, and then it reaches a stable stage. Decline trend is emerged after that. The half-length, spacing and conductivity of fractures are also major factors influencing the production performance. The optimum intervals of these factors are all existed.

A case study is conducted based on real geologic model afterward to optimize the technological parameters during coupled liquid CO₂ fracturing–huff and puff treatment, which has valuable guiding significance for design and optimization of field operation.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018