Successful Sweep Efficiency Improvement of Horizontal Wells in a High Temperature and High Salinity Reservoir by In-Depth Waterflood Conformance Control using Low-Density Gel Particles

Abstract

AbstractHDX oilfield is located in Tarim Basin (China) and operated by PetroChina. Horizontal wells are used to develop some reservoirs. Due to high permeability heterogeneity, injection water early breaks through, resulting in a poor sweep efficiency. Conformance control is considered as the most suitable technique for sweep improvement, but such treatment in horizontal wells is more difficult than in vertical wells. Moreover, high temperature (112 ℃) and salinity (290,000 mg/L) increases extra difficulty in the treatment. Because of high temperature and high salinity, dispersed gel (DG) particles were suggested given that they are more insensitive to harsh environments than in-situ crosslinked gels. Considering wide well spacing and discontinuous interlayer, in-depth conformance control using a large volume of gel particles was proposed. To achieve in-depth migration, gel particles should have a slow expansibility and a high deformability. For horizontal well, particles sedimentation in horizontal section is a challenging issue. Therefore, the density of gel particles should be enough low to be well suspended. To meet all these requirements, eventually delayed expansion in water, low-density, highly deformable DG particles were synthesized.The first application was started at October 2016 and finished at June 2017. Multiple slug injection with different particle size and concentration was designed, and gel particles-alternating-water injection was implemented. Incremental oil production response was observed at December 2016 since the second slug injection started. Until June 2019, incremental oil was 45,255 tons, and the input-output ratio is about 48.59. Considering this huge success, the second treatment in another well was implemented from July to September 2019. The incremental oil after 8 months was 4,870 tons, and the treatment continues to be effective until 2022. Moreover, the first treatment is still effective after 3 years, which proves the treatment a great technical and economic success. This paper presents the idea of the operation design of low-density DG particles for in-depth conformance control in horizontal wells. Furthermore, how to precisely evaluate treatment effect are discussed in detail based on production performance together with water injectivity, pressure index, and wellhead pressure drop curve in the injection well.This paper not only presents the idea using low-density gel particles with multistage injection process of gel particles-alternating-water for in-depth conformance control in horizontal wells, but also summarizes important experiences for successful field operation design and control, which will give an updated framework and an important guidance for in-depth conformance control treatment in horizontal wells under high temperature and high salinity conditions.