Carbonate Reservoir Facies and Multi-Pore System Analysis Using LWD Resistivity Imager Acquired During Pressurized Mud Cap Drilling - A Case Study Offshore Sarawak, Malaysia

摘要

Facies and multipore system analyses are required for reservoir modeling as part of the field development plan for one of the largest non-associated gas bearing carbonate fields in Malaysia. To overcome the reservoir challenges, the wells in the field were drilled using the pressurized mud cap drilling (PMCD) technique, which significantly affected the type and quality of the necessary petrophysical data acquired for reservoir evaluation. This technique also added challenges when trying to standardize an evaluation technique for all wells in the field. The well under study was logged using a resistivity imager tool while drilling with an exceptionally high image quality, which enabled the required analysis to be performed. Structural and stratigraphic analyses were performed using conventional techniques, and a correlation was made with the core analysis from a short cored section in the well. The multipore system analysis was performed using a technique that transfers the image resistivity to a porosity map and breaks it into micro, mezo, and macro pore volumes by using one of several mathematical or statistical methods. The reservoir permeability was estimated by using a rock fabric technique that takes into consideration the contribution of inter-particle and secondary porosities. Image-derived lithofacies, reservoir units from pore system analysis, and the electrofacies obtained from the quad-combo data acquired while drilling were used to characterize the reservoir and classify it into geologic and petrophysical units. A comparison between the various techniques was made, whereby similarities and discrepancies were analyzed to plan a standard workflow for the remaining the wells in this field. This paper presents the difficulties encountered when using the data acquired under such a challenging drilling technique and the proposed workflow for reservoir characterization; it also uses a case study from offshore Sarawak, Malaysia to illustrate the advantages and disadvantages of the technologies and techniques used.