Using Core, Image Logs, Tracer, Production, and Mud Logs to Support the Development of Low-Permeability Limestone Oil Fields: A Case Study from the Pearl River Mouth Basin, China

Abstract The A oilfield has two sets of reservoirs, reef limestone (J10A) and bioaccumulated limestone (J10B). The data from 2 vertical exploration wells in the middle and northern oilfield show that the formation belongs to medium-porosity and low-permeability porous limestone formation. The oil field was decided to be developed in the form of multi-branch horizontal wells, with more wells in the J10A formation with a high oil column than in the J10B formation with a relatively low oil column. There were two major problems in the early stage of development. First, there was great uncertainty in the quality and distribution characteristics of the formation in J10A. Two pilot wells showed that the reservoir in J10A in the southern part of the oilfield was thinning, the reserves were reduced, and the development wells arranged in J10A in the south could not be completed. Second, the first batch of horizontal wells generally contained water (10-20%), with the highest water content reaching 80%. Timely identification of high-quality reservoirs and implementation of water-producing formation characteristics become the key to continuing to implement and adjust development strategies. Make full use of the core and logging data of the vertical exploration well to implement the characteristics of the reservoir and the logging curve identification method. By comparing the core porosity and permeability, thin sections, and capillary pressure, analyze the reservoir quality and establish the logging response characteristics of reservoirs of different qualities. At the same time, use the electrical image logs, 3D geochemical mud logs, and hydrocarbon phase mud logs in the horizontal branch well to analyze the development characteristics of fractures and dissolution pores. Combined with production, tracer, geological guidance data and well position in the reservoir, analyze the characteristics of water-producing formations and logging identification methods. Based on the tracer results and production data, the reservoir matrix pore quality and fracture development characteristics are comprehensively considered to implement the characteristics of high-quality reservoirs and logging identification methods. The electrical image logs in the horizontal wells showed high-angle, small-size, low-density fractures that were not observed by electrical image logs in vertical exploration wells, which changed the understanding of the formation quality and formation water production in the area. Through the comprehensive application of multiple data such as logging, core, production, tracer, and mud logging, the basic formation quality characteristics, the development characteristics of fractures and dissolved pores, and their logging expressions were implemented; at the same time, the characteristics of water-producing formations, logging identification methods, and reasons were clarified. The characteristics of high-quality formation and logging identification methods are used to guide the deployment of horizontal wells and geological guidance work while drilling. Subsequent production data verified the reliability of reservoir quality evaluation. The combination of core, logging (image logs + conventional logs), production (production + tracer), and mud logs (3D geochemical and hydrocarbon phase) under specific oilfield and production stage promptly and effectively solved the problems in the oilfield development process. This idea cleverly maximizes the association between application data to solve actual production problems. It helped the oilfield to successfully implement 15 (multi-branch) development wells under the condition of reduced reserves, and the production reached the requirements of the development design plan, and smoothly entered the production stage.