Tight Gas Petrophysical Challenges in Saudi Aramco
- David Forsyth (Saudi Aramco) | Nedhal Mohammed Al Musharfi (Saudi Aramco) | Anas M. Al Marzooq (Saudi Aramco)
- Document ID
- Society of Petroleum Engineers
- SPE/DGS Saudi Arabia Section Technical Symposium and Exhibition, 15-18 May, Al-Khobar, Saudi Arabia
- Publication Date
- Document Type
- Conference Paper
- 2011. Society of Petroleum Engineers
- 1.2.3 Rock properties, 2.5.4 Multistage Fracturing, 1.12.3 Mud logging / Surface Measurements, 5.7 Reserves Evaluation, 5.5.2 Core Analysis, 2.4.3 Sand/Solids Control, 5.5 Reservoir Simulation, 5.6.1 Open hole/cased hole log analysis, 1.11 Drilling Fluids and Materials, 6.5.4 Naturally Occurring Radioactive Materials, 1.6 Drilling Operations, 5.2 Reservoir Fluid Dynamics, 5.2.1 Phase Behavior and PVT Measurements, 5.1.5 Geologic Modeling, 1.14 Casing and Cementing, 5.8.2 Shale Gas, 5.8.1 Tight Gas, 4.1.2 Separation and Treating, 4.6 Natural Gas, 5.6.2 Core Analysis, 1.6.9 Coring, Fishing, 3 Production and Well Operations
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Recently, Saudi Aramco upstream activities in unconventional gas, and in particular tight gas sands, have been identified as a focus area. Integral to understanding the potential of tight gas as a resource, is an understanding of the petrophysical characterization of tight gas intervals. This paper presents a review of the petrophysical challenges in the evaluation of tight gas intervals encountered within an existing producing field producing from formation U. This formation can be highly variable and although it can be highly productive, in some areas the geology has produced poorer reservoir quality rock. Production from wells which penetrate these areas can exhibit "Tight Gas?? characteristics. Core and log data from existing fields are abundant and cover both good and poorer quality reservoir intervals. The factors which impact the evaluation of these "Tight Gas?? intervals, in this relatively well sampled environment, can be generalized to the evaluation of less well studied tight gas formations. The results of this review identify many areas where current techniques and tools fall short of providing an adequate characterization. In particular, the quantification of mineralogy and diagenesis is seen as important, as is the quantification of saturations and accurate measurement of micro-Darcy permeabilities. Areas where current techniques require improvement are highlighted and projects that are in progress to address these issues and improve the evaluation of tight gas are detailed. One area which is highlighted as holding potential is rock typing, which can categorize different types of tight gas interval based on clay content or mineralogy. Three wells have been selected for a fracturing exercise as a proof of concept to assess the production potential. The results of the fracturing exercise are presented relative to the petrophysical evaluation of these wells.
The identification and evaluation of the reservoir potential of tight and unconventional gas reservoirs has recently become a priority focus area in Saudi Aramco (Al Falih1). As part of that effort, two main thrusts are being explored. The first main focus is being expended on the exploration front to discover and appraise new areas for their tight and shale gas potential. This effort is ongoing and is in its preliminary exploration phase. A second thrust where effort is being expended is the development of tight gas in Saudi Aramco's core area. Within existing producing fields which penetrate the K, U and J geological formations, there are areas where the reservoir can be less well developed. In particular, the Early Permian/Carboniferous eolian clastic intervals of the U formation present a particular challenge given the high lateral variability. The U formation is composed of alternating beds of red sandstone, siltstone, mudstone and conglomerate deposited in an alluvial fan, dominated by braided-river system, eolian and playa systems, which provide much potential for the study of tight gas sands. Production from wells that penetrate such poorer areas can be disappointing and stimulation is required to produce a viable well. As such, these intervals constitute a valuable tight gas resource with its own development and evaluation challenges.
As a small part of the appraisal effort of these tight gas areas, candidate wells penetrating the Unayzah formation were identified for application of Slanted/Horizontal multistage fracture stimulation as part of a proof of concept exercise (Buhidma2 ). Since these wells were originally planned as standard development wells into the U, neither special log nor extensive core data were planned. Consequently, it was difficult to substantiate the evaluations of these wells with comparative core and other data.
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