On the Quest for Ester-Base Mud System Impact on Data Acquisition

Abstract

Abstract Oil-Base Mud (OBM) systems have been used in the oil and gas industry for many years. Historically OBM systems have contained aromatic compounds. Environmental concerns linked to the use of OBM pushed the industry to develop Synthetic-Base Mud (SBM) systems with no aromatic content. This paper focuses on the use of ester-base mud (EBM). EBM was originally used in the top-hole sections of wells. It is now extensively used to drill the complete range of exploration, development, water source and water injection wells. This paper will demonstrate that EBM has a significant impact on well measurements (FEWD and wireline logging, mud logging, coring, etc.) when compared to Water-Base Mud (WBM) or traditional OBM. Examples derived from offshore and onshore fields in Nigeria will be presented. Local efforts to investigate the effect of EBM, have been carried out in Nigeria by Oil and Service companies. These results seem to indicate that this effect causes a modification of the mud filtrate invasion profile within the formation and results in a complex interaction with the fluid in place. Adverse effects have been observed which have consequences on formation evaluation data and the subsequent static and dynamic reservoir evaluation. A major concern is that Original Oil In Place (OOIP) calculations are systematically reduced. Therefore, on critical wells where formation evaluation is a key issue, the choice of such mud systems needs to be balanced with the potential loss of geological and petrophysical information and the anticipated reduction in drilling cost. A comprehensive study, coordinated by a special interest group, needs to be initiated on a larger scale by the companies concerned. The objective of the study would be to understand the physics and chemistry of SBM on rocks and formation and develop corrections for log and core measurements. This study would benefit the worldwide users of SBM drilling fluids. This paper will discuss the observations and propose a program to better understand the phenomenon and improve formation evaluation accuracy.