AAPG/EAGE Workshop on Tight Reservoirs in the Middle East

Conventional hydrocarbon resources have been associated with pre-Devonian petroleum systems across the globe, including the Neoproterozoic–Infracambrian Huqf Supergroup of the Oman basin, the Riphean - Vendian sequences of East Siberia, the Cambrian of the Sirte basin, the Ordovician of the Tarim basin, and the Silurian Qasaiba of Saudi Arabia. Although individual accumulations can be quite significant (e.g., Hassi Messaoud has proven reserves of ~6.4 billion barrels), the relative importance of pre-Devonian-derived oils is limited compared to the global conventional resource-base. With growing interest in unconventional resources, the relative importance of these systems is expected to increase as plays such as the Ordovician Utica Shale of the Appalachian basin, the Cambrian of China, and the Silurian of Central and Eastern Europe develop.

Many hydrocarbon reservoirs such as tight gas sands composed of low porosity (1%-10%) and microdarcy-scale matrix permeability (1-60μD). Such reservoirs unless they are naturally and heavily fractured are hard to develop without proper stimulation. Simulation of the reservoir is directly driven by reservoir geological and geomechanical properties. Hence, it is important to characterize the reservoir not only in terms of reservoir matrix properties but also fracture and mechanical properties.

Source rocks occur in many basins of the world, however differentiating which are suitable unconventional reservoirs requires the application of sound petroleum exploration concepts. Unconventional exploration concepts, although similar to conventional exploration, have many niche techniques. Utilizing these concepts properly can reduce upfront and development risk.

Early recognition of a fractured reservoir and an estimation of its rock characteristics, such as porosity and permeability, will influence the location and number of subsequent development wells and, therefore, is of major economic significance on the future development of the field.

Multistage Stimulation (MSS) has often been viewed as simply running a completion string followed by pumping services. However; the early attempts at uncemented, openhole multistage stimulation completions in the Middle East were met with mixed operational success. It became clear that the standard completion approach and stimulation procedures could not be directly applied. A new set of best practices would be required in these Middle East wells that included a new and integrated, multidisciplinary approach that took a step backwards in the process to the pre-drilling phase, focusing on well planning optimization to maximize the multistage completion technique and ultimately the well productivity.

This presentation focuses on the evolution of the post-drilling phase of the oilfield. We will begin with the conventional single stage vertical market, and transition to the contemporary multi-stage high-efficiency landscape. An analysis of the regional infrastructure based around the transportation of required materials in a high consumption hydraulic fracturing market will be discussed with examples given. Alternative material sources will be discussed, and weighted based on their ability to effect the end product to the customer. Lastly, methods to track and improve the efficiency of the service company/operator partnership will be presented and discussed.

Hydraulic fracturing is the most successful method of production enhancement developed by the petroleum industry. Unfortunately, people involved in hydraulic fracturing often tend to focus on getting the proppant in the ground, an accomplishment by itself in many places, and forget the final target of production enhancement. To make matters worse, many companies leave the evaluation of the resulting performance to other people than the people who evaluated the fracture treatment.

Marginal and unconventional reservoirs can have lots of resource potential and reserves, but may require horizontal well drilling, and/or multiple stage hydraulic fracturing to achieve economic production targets. This type of strategy is more expensive than conventional method(s) and is proven in some circles as potentially risky and many of these risks must be addressed and mitigated. In an effort to reduce risks and costs associated with the exploration process, a new stimulation strategy has been adopted for unconventional and tight intervals to explore and appraise these intervals using vertical wells and fir for purpose fracturing prior to going to horizontal wells.

Oman’s rapid domestic demand growth for gas, primarily for power generation, significant LNG sales contracts, and the petrochemical industry, will be met in the near future with a decline in conventional gas production. The supply shortfall may be met by Tight and Unconventional Gas, with its large volumes and long-term potential. To secure mid-long term supply Petroleum Development Oman (PDO) is executing an appraisal programme in North Oman focussing on the Amin Fahud Basin Tight Gas sandstones with porosities ranging from 3 to 10% and (ambient) permeabilities from 0.001 to 1 mD.