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Abstract The development drilling operations in the Maydan Mahzam Upper/Mid-Jurassic reservoirs involve targets in between intensively faulted compartments with thin zones comprised of facies that vary laterally. The structural dip varies across the drilled horizontal sections to add to the structural uncertainties. In this paper, three selected case studies from structurally complex areas in Maydan Mahzam are presented to illustrate the application of the advanced horizontal well placement process for the purpose of properly draining the oil in these areas. In all these cases, the horizontal sections where successfully placed. Drilling in these areas was avoided in the past due to their highly structural uncertainties. The advanced technology used in the well placement process comprises drilling with full suite of LWD logs, real-time data transmission from the well to the office, and seismic follow up. The well placement was carried out by an integrated team from the preparation phase and continued during drilling the well till the completion phase. The success of the well placement process has been enhanced by utilizing the structural evolution knowledge of Maydan Mahzam field in particularly the occurrence and orientation of the two sets of faults. The utilization of the depositional progradation model of the producing rock types had contributed to the well orientation and placement optimization. Introduction Maydan Mahzam is an offshore mature field lying in the shallow water in the Arabian Gulf some 102 kilometers east of Doha (Figure 1). The Maydan Mahzam structure at top Upper and Middle Jurassic reservoirs consists of an elongated domal structure which is developed over a deep-seated salt dome. The field was discovered in 1963 when commercial oil rates were tested in the Arab D reservoir (Figure 2). In subsequent appraisal wells, it was found that other reservoirs in the field also contained significant oil reserves. In both Qatar and throughout the Arabian Gulf, the Jurassic reservoirs are mainly composed of shallow-normal water carbonates. The Maydan Mahzam structure is complicated by existence of a complex NW/SE and NE/SW orientation fault system, varying structural dip (1 to 9 degrees), and the existence of several unconformities across the Jurassic formations. This pattern of fault development reflects the significance of the effect of the nearby Zagros Belt movements and the halokinetic growth of the field during the Cretaceous and early Tertiary1 & 2. The faulting is more intensive in the crestal and southeast parts of the structure where the three successful horizontal wells were recently drilled. These wells were selected as case studies to demonstrate the successful well placement application. The technology used for well placement includes: integration of the use of the various LWD logs through the real-time transmission, calculating the apparent dip along the well and correlation with the nearest well across the horizontal section. The well placement was optimized by comparing the well trajectory with seismic. The sedimentological modeling of the targeted reservoir was also utilized. The early preparation and close monitoring of the well were carried out by integrated teamwork. The successful geosteering in this highly complicated structure is the subject of this paper. |
