Successful Field Application of Delayed Water-Swelling, Flexible Gel Particles for In-Depth Waterflood Conformance Improvement in Wide Spacing of Wells with High Temperature and High Salinity

Abstract

The HD Oilfield, operated by PetroChina, is located in Tarim Basin. It is characterized by high temperature (112 ℃) and high salinity (291000 mg/L), and developed by wide spacing of wells (average 700 m). High vertical and areal heterogeneity lead to early water breakthrough and a poor water sweep efficiency. Effective conformance control is urgently needed, but harsh reservoir conditions, wide well spacing, and discontinuous interlayers pose great challenges for conformance treatments in this field. Because of wide well spacing and discontinuous interlayers, water channeling and crossflow in in-depth part of reservoir could still occur after conformance treatment. To prevent this, in-depth conformance improvement treatments with injecting large volumes of low-cost profile control agents were proposed. To achieve this goal, we designed delayed water-swelling, flexible gel particles that have high deformability and elasticity. Simultaneously, to meet the harsh reservoir conditions, gel particles were designed to have long-term tolerance to high temperature and high salinity. The first treatment was implemented in May 2016, and the total incremental oil by June 2019 was 17347 tons. The treatment validity is more than 36 months, and it keeps being effective. Until now, 9 treatments have been finished. The total incremental oil is 102100 tons until May 2020, and the increment is still going on. The input-output ratio for these 9 treatments is about 8.45, which indicates the treatments were an economic and technical success. In this paper, first we describe the design of gel particles and their properties evaluation by extensive experiments, including water-swelling ability, long-term tolerance to high temperature and high salinity, elasticity, tenacity, injectivity, selectivity, plugging ability, and scouring resistance, etc. Then, we present operation design and control in the field, which is especially important for the success of these treatments. Furthermore, according to production performance as well as the wellhead pressure drop curve, pressure curve of water injection, and water injectivity in injection well, treatment results are discussed in detail to evaluate if the treatment is successful or not. Finally, several important experiences with respect to how to do operation design and field control are summarized. This paper documents a successful case history of in-depth waterflood conformance improvement in wide spacing of wells. These successful field cases together with summarized experience will provide a detailed guide and an updated framework for conformance improvement treatment for operators. In addition, this paper presents an alternative agent, i.e., delayed water-swelling, flexible gel particles, for in-depth waterflood conformance improvement in high temperature and high salinity reservoirs.