Using mud gas while drilling analysis to predict reservoir fluid characteristics of the Zubair reservoir in north Rumaila field, southern Iraq

Abstract

Understanding the properties of fluids present in an oil and gas reservoir is important for the exploration and development of a field. Detecting hydrocarbons early on allows for a more accurate analysis of the reservoir’s fluid characteristics and helps minimize uncertainty in reservoir assessments and future field planning. Two methods commonly used in the oil and gas industry for this purpose are gas while drilling (GWD) and wireline logs analysis. However, each method has its own limitations and advantages, so an integrated approach that combines these methods can provide more accurate and comprehensive information about fluids in a reservoir. The main objective of this work is the desire to develop an understanding of GWD interpretation in the Zubair Formation in North Rumaila oilfield, southern Iraq using real-time chromatographic analysis of hydrocarbons can be used to effectively characterize the reservoir fluids. Our research incorporates three wells from North Rumaila oilfield in southern Iraq, focusing on the “Zubair Formation” which serves as the main target formation for hydrocarbon. The datasets consist of drilling parameters, mud logging data, LWD/wireline log, geological reports, PVT results, wells test data, and formation pressure data. Total gas and chromatograph components reading were synchronized with depth and corresponding lithology. All of the data were checked for potential errors that may have been caused by factors such as drilling mud properties and additives, borehole conditions, and the nature of the formation, etc. Gas quality ratio (GQR) was calculated in order to determine any contamination in the data, whereas gas ratio analysis was conducted to interpret gas readings using the following methods: wetness, balance, character ratio, pixler ratio, fluid saturation, reserval ratio, and an additional light–gas ratio plot. Gas analysis results were compared with production test data and suggesting that this method is reliable and capable of helping to justify a decision for further drilling action. This study explains that integrated gas while drilling (GWD) analysis can be a powerful method for reservoir fluid characterization within minutes after the Zubair reservoir was drilled using real-time mud gas data. In addition, our interpretation suggests that this method is useful to identify fluid characterization and contacts, assisting pressure test (permeability), selecting pay zone, and distinguish between non-productive and productive hydrocarbon.