This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 164008, ’Adopting North American, Multistage Fracturing and Horizontal Completion Technologies Starts To Unlock the Amin Tight Gas Formation in the Sultanate of Oman,’ by Robert Clark, SPE, BP, and Kevin Mullen, SPE, and Stevanus Kurniadi, Schlumberger, prepared for the 2013 SPE Middle East Unconventional Gas Conference and Exhibition, Muscat, Oman, 28-30 January. The paper has not been peer reviewed.
The careful planning and successful execution of a multistage-fracture-stimulation completion in one of the first horizontal wells (KZN-F) drilled in the Amin formation in north central Oman instigated a step change in initial production rate and long-term deliverability from this tight-gas-sandstone reservoir. The operator and service company worked as a team, modeling the fracturing program after North American practices.
Introduction
Most of the natural gas in the Amin formation is locked up in low-permeability, extremely hard sandstone formations in very deep reservoirs. Drilling times of 3 to 4 months are typical for vertical wells, and fracture stimulation is necessary.
BP acquired the concession from the Sultanate of Oman in 2007 to engage in an appraisal of the block (shown in Fig. 1). Following appraisal, a full field-development license may be granted to develop the block. The objective of the appraisal project is to evaluate the delivery potential of gaseous hydrocarbons from four reservoirs: Barik, Miqrat, Amin, and Buah. There were two wells drilled by BP that tested the Amin formation in the field before this investigation. The KZN-C well was stimulated with a conventional crosslinked-gel fracture treatment, and the KZN-E Amin well was stimulated by use of a hybrid technique. The only other fracturing technique that had not yet been introduced to the Amin formation was a high-rate water fracture (HRWF), also known as a slickwater fracture. This technology, widely used in North America, had originally been planned for use in the Amin reservoir and had already been used successfully in the Miqrat reservoir.
Pumping and chemical costs are lower for an HRWF than for crosslinked-gel fracture treatments.
Challenges and Solutions
Zone Selection. Six target intervals were selected for flow testing in the KZN-F well, with the goal of evaluating the efficacy of different reservoir-access and stimulation technologies, as well as determining which formation conditions would contribute to flow. These intervals were identified by use of a combination of mud logs, conventional openhole logging, and a microimaging log. Gamma-ray, resistivity, and porosity logs were used to differentiate zones in the Amin reservoir that might present more-promising targets. The microimaging log proved to be valuable for identifying fractures in the reservoir that could be targeted for stimulation. Fractures were categorized as faults, natural fractures (cemented or uncemented), or drilling-induced fractures on the basis of their appearance on the log. Fig. 2 illustrates some of the data available from the microimaging log used to target key wellbore objectives.
