The first phase development of the Athel formation in South Oman relies on massive hydraulic fracture stimulation to realise economic production rates from micro-Darcy rock. It has been recognised that the size, shape and direction of the hydraulic fractures are key parameters in the prediction of well performance, optimum well placement and optimisation of fracture design. In view of the highly laminated, intensely structurated geology, an early assessment of flow barriers and dynamic reservoir behaviour will also be crucial to managing long-term recovery of the significant Athel reserves. In order to acquire substantial data addressing each of these issues, an integrated permanent downhole data acquisition system (PDDA) is being installed in the Phase I production wells. The system utilises a unique combination of tubing conveyed gauges and triaxial geophones to deliver real-time bottom hole pressure/temperature and microseismic data throughout both stimulation and production. The first well equipped with the PDDA system was fracture stimulated in May 2000. This paper presents initial results, including interpretation of the microseismic data to determine fracture azimuth and dimensions. The ongoing PDDA project, leading to integration of microseismic data recorded in offset wells and the acquisition of long-term flowing bottom hole pressure and build-up data is also discussed and comments made on the general oilfield applicability of such systems. Introduction The Al Noor reservoir in South Oman - discovered in 1989 - is a 400m thick, tight, microporous silicilite slab encased in salt at a depth of 4000m. The crestal area has average matrix porosity of 20% and matrix permeability of 0.001–0.1 mD. Initial oil in place is estimated to be 210 million m3. In the absence of aquifer support, primary recovery under depletion drive is expected to be 7–8%. Unstimulated flow rates have been measured at up to 110 m3/d. However, after massive propped hydraulic fracture stimulation, well ALNR-6 was tested at initial rates in excess of 1200 m3/d. Key uncertainties in the economic development of the Athel reserves are the sustainability of commercial flowrates and the viability of enhanced oil recovery (EOR) schemes. Wellbore image logs and core studies reveal micro-laminated structure and a complex network of cemented natural fractures at the milli- and centimetre scales (Fig. I). At the seismic scale (>50 m), a large number of partially and fully penetrating faults have been interpreted. The unknown influence to flow of these barriers - and others not resolved at intermediate scales - leads to considerable uncertainty over the long-term producibility of the reservoir. EOR through water or gas flooding would require pattern drilling of close-spaced injection and production wells, each of which would be hydraulically fractured. Since the Athel slab is floating in salt, no clear horizontal stress regime has been determined. The orientation and geometry of induced hydraulic fractures - critical to optimising fracture treatment design as well as to EOR well placement (Fig. II) - are therefore difficult to predict. In view of these and other uncertainties, Petroleum Development Oman LLC (PDO) has begun a phased development of the Al Noor accumulation. Phase I comprises a 1500 m3/day production facility served by seven development wells. In order to make an informed investment decision regarding further development, extensive data gathering is planned. As part of this, the Athel Asset Team has elected to install integrated permanent downhole data acquisition (PDDA) arrays in the Al Noor development wells to record bottom hole pressure and hydraulic fracture induced microseismicity. The first installation was completed in well ALNR-7 in April 2000. Fracture stimulation was carried out in May.
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