Bridging the Gap: A Pathway to Robust Rock Strength Modeling and Reliable Sand Production Risk Assessment in Thermal Steam Project

Abstract

Abstract Thermal steam project has been successfully implemented in Haradh formation in A-East field in the south of the Sultanate of Oman. This project was developed outside the crest and expanded further to the north. Sand production control was identified as a potential risk; therefore, a sand prediction model was required to assess the rock strength at both hot and cold operating production conditions. Due to the large uncertainty in rock strength for Haradh at high temperatures, a dedicated fit-for-purpose geomechanics program was executed for an appraisal well drilled in the field. The main objective was to determine the strength characteristics of Haradh at room and elevated temperatures, which would help to assess the reservoirs stability during the thermal steam injection process. This paper outlines (i) the results of Geomechanical laboratory analysis, (ii) elastic and physical properties from log data and (iii) generated log-derived rock strength model. Large rock volume XL-Rock Rotary Sidewall (SWC) coring was carried out in X-well across the full depth range of Haradh oil column. The Computerized Tomographic scanning images were used for quality control and selection of the best core plugs for testing. Unconfined compressive strength (UCS) tests were performed at atmospheric confining stress (confining pressure is zero) and "as received" condition at room (20-25 °C) and elevated (200 °C) temperatures to simulate the operation conditions during steam injection. Thin section petrographic and point counting analysis was conducted to study the impact of mineral contact on the UCS. Empirical relationships were established between core measured UCS and log data to develop UCS profile across Haradh formation. UCS results show medium rock strength ~ 13 −17 MPa of Haradh sandstone at room temperature. As the test was performed at high temperatures, the UCS value shows a drastic drop in the rock strength of more than 50% reduction (range between 3.16 to 6.84) which might indicate a potential risk of rock failure at high temperatures. The comparison between the laboratory measured UCS and the profiles obtained from the empirical models show a reasonable match specially with the Petroleum Development Oman (PDO) correlation. The study results show that Haradh rock's strength may decrease during thermal steaming operation, which could potentially lead to reservoir instability and failure. A more detailed evaluation is recommended to assess this risk and investigate the impact of temperature induced stresses on sand production using FIST (Fully Integrated sand prediction tool) rock failure model.