A Novel Approach to Overcoming Fluid Identification Challenges in Highly Heterogenous Saturated Clastic Reservoirs

Abstract Accurate fluid identification is a crucial element in reservoir understanding and characterization especially in saturated reservoirs, where free gas and oil both exist in the reservoir. The delineation of gas/oil contact is highly dependent on fluid identification from well logs and formation testing. For well logs, the mostly common practice in the industry for gas and oil identification is through the density-neutron logs as their signatures in the two distinct phases is very differentiable most of the time. However, this could be challenging to recognize in certain environments such as in highly heterogenous sandstone reservoirs. It gets even more challenging to distinguish gas from oil from neutron-density logs when clay is present within pay zones introducing high uncertainty in various fluids identification. Another layer of complexity is added when this environment contains light oil which has less contrast with gas compared with heavier oil. This paper discusses a new integrated approach to address this fluid identification challenge utilizing multiple logging methods, such as neutron far and near detectors raw data, acoustic shear and compression raw data, nmr T1 and T2, clay content, and resistivity measurements. The paper also presents how the abundance of logs available are leveraged to identify trends within pay zones that could potentially help in distinguishing oil form gas; and results are proven with fluids sampling. This innovative approach which integrates multiple logs reduces the uncertainty in gas identification and can help eliminate fluid sampling in heterogenous sandstone reservoirs, having a potential to cost reduction. The outcome plays a key role not only in enhancing reservoir characterization but also guides new wells placement, and increases confidence in logs signatures. The results of this approach increased the confidence in identifying gas zones by 85%.