Geothermal Rocks Compressive Strength Evaluation During Drilling Operation

Abstract

Geothermal well drilling design is considered based on the rock strength inside the wellbore. One of rock strength parameter that analyzed in this study is rock compressive strength. Several methods have been developed to determine rock compressive strength by using laboratory core sample test. Empirical correlation to calculate rock compressive strength by using drilling data has been widely developed in oil and gas industry. Meanwhile, those empirical correlation has not yet developed and required adjustment for geothermal field. Those calculation are can be used as the initial interpretation, particularly in exploration wells, by using real-time geothermal drilling data processing.
This study was conducted to predict the rock compressive strength in water dominated geothermal field using the analysis of drilling data in Mud Log Unit (MLU). The rock compressive strength is approached by analyzing the drilling parameter trend such as Rate of Penetration (ROP), Weight on Bit (WOB), and Revolution per Minute (RPM). Corrections are performed by analyzing the bit used in each section, geothermal rocks lithology, wellbore design, and drilling operation conditions.
Rock compressive strength prediction can be done by using the reference of common geothermal rocks physical properties encountered in association with volcanic area such as andesite, breccia, tuff, and rhyolite[4]. The correlation between rock compressive strength and drilling parameter is evaluated at particular section. Those evaluation can improve the performance and future development drilling design.