AAPG GEO 2010 Middle East
Geoscience Conference & Exhibition
Innovative Geoscience Solutions – Meeting Hydrocarbon Demand in Changing Times
March 7-10, 2010 – Manama, Bahrain
Miqrat Formation (Cambrian) a Challenging, Tight Gas Play in Prograding Sheetflood Sands, Sultanate of Oman
(1) XGM/1, Petroleum Development Oman, Muscat, Oman.
(2) Besly Earth Science Ltd., Newcastle Under Lyme, United Kingdom.
(3) XEO/1, Petroleum Development Oman, Muscat, Oman.
The Miqrat Formation (middle Cambrian, Haima Supergroup) of North Oman is an identified deep, tight (low permeability) gas reservoir that was deposited in an arid to semi-arid continental setting, consequently it is biostratigraphically barren. It is dominated by finely interbedded, red-brown shales intercalated with argillaceous and feldspathic/micaceous very fine- to fine-grained sandstones and siltstones. These were deposited in alluvial and playa/lacustrine to sabkha environments with minor aeolian intervals. The formation offers a variety of geological and well engineering challenges, largely related to its depositional setting and age.
Facies relationships were controlled by a spectrum of sedimentary processes operating at different scales. Important constraints, at a basin scale, are wet/dry climate cycles within a framework of varying sedimentation rates and accommodation space. Developing accurate subsurface depositional models is hampered by poor seismic resolution and a lack of reliable correlation events to constrain palaeogeographic reconstructions and tie these to field-scale depositional models. With limited well control, absence of biostratigraphic markers and non-unique wireline log characteristics, correlation of similar-appearing sheetflood sands may be erroneous as these may correlate with time equivalent flood margin or muddy playa deposits. The identification of correlatable markers is, therefore, significant. Pilot studies applying chemostratigraphy suggest that this technique may prove to be a useful tool for subdividing the Miqrat Formation.
Regional and in-field Miqrat well data, integrated with outcrop studies, provide the main input into geological models and the basis for play maps and static reservoir modelling. However, many challenges exist, especially for early appraisal activities. These include reservoir productivity identification and “sweet-spotting”; assessment of gas mobility during drilling; petrophysical evaluation (saturation/mobile phase identification). Additionally, the role of fractures needs to be understood in achieving commercial rates, whilst fraccing and testing require innovative solutions to provide optimal stimulation and reservoir assessment, respectively. Project attractiveness may rely on improvements in seismic imaging, improved play models, better prediction of reservoir quality/fracture networks, together with a better understanding of charge history and improved offtake rates.