Optimization Chemical Flooding Methods to Enhance Oil Recovery of Strong Heterogeneity, High Temperature and High Salinity Reservoirs - Case Study of Shengli Oilfield

Abstract

Abstract Chemical flooding usually cannot achieve good oil displacement effectiveness in strong heterogeneity, high temperature and high salinity(SH/HT/HS) reservoir. Through a typical SH/HT/HS reservoir in Shengli Oilfileld, this paper builds a screening method to select the optimal chemical flooding approach with best economic effectiveness for SH/HT/HS reservoir. Numerical simulation based on field data is used to screen chemical flooding approaches. First a novel index called Gini coefficient of the injection profile(GINIP) is proposed to preliminarily select chemical flooding approaches. Different chemical flooding approaches have different GINIP turning points. Oil recovery drops sharply when GINIP exceeds turning points. And then economic effectiveness is considered. Economic effectiveness is expressed by the ratio of enhanced oil weight and chemical agent cost(t/dollar). Salinity, calcium-magnesium content and temperature influence the economic effectiveness of chemical agent. So an optimal chemical flooding is selected for specific SH/HT/HS reservoir by the above two steps. According to different agents, heat-resistant and salt-tolerant chemical flooding can be divided into Surfactant-Polymer(SP), SP-Preformed Paticle Gel(SPPG) and Polymer-Preformed Paticle Gel(PPPG). The GINIP turning point of SP is 0.76. SPPG is 0.82 and PPPG is 0.85. The GINIP of GDCR1 block in Shengli Oilfield is 0.6. So SP, SPPG and PPPG can all be applied. Salinity of GDCR1 block is 10000mg/L. Calcium-magnesium content is 100mg/L and temperature is 70°C. The economic effectiveness of SP is 16.34t/t. SPPG is 18.46t/t and PPPG is 15.02t/t. So SPPG is the optimal chemical approach for GDCR1 reservoir. In recent five years, SPPG flooding applied in GDCR1 block enhanced current oil recovery 5.6%(total oil recovery over 60%) and decreased maximum water cut over 19.7%. Compared with other nearby same blocks, this performance is very good. This indicates that the screening method presented in this paper is effective and accurate.