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Middle Eastern carbonate petroleum reservoirs exhibit a range of heterogeneities which consist of variable combinations of primary stratigraphic and secondary diagenetic and structural characteristics. These produce diverse permeability architectures which can exert a profound influence on reservoir performance during secondary recovery. Of particular importance are laterally persistent discrete zones of elevated permeability (DZEP) that typically make up a volumetrically minor proportion of the reservoir yet show disproportionately high fluid inflow or outflow. The stratigraphic, diagenetic, and structural origins of elevated permeability in Middle Eastern carbonate reservoirs are considered here and the consequences of such features for reservoir performance are discussed. The term DZEP denotes geological sources of elevated permeability at least an order of magnitude greater than background reservoir properties. Stratigraphically organised DZEP comprise coarse-grained layers, event beds or parasequence tops or bases in neritic or platform interior settings. Other origins include bioturbated layers, grainy clinothems, and bed-scale, grain-size variations in shoal deposits. Diagenetic DZEP are typically dissolution horizons with mouldic and touching-vug pore networks or dolomitized intervals which often overprint stratigraphic DZEP. Structural DZEP include individual faults, fracture corridors, and fracture concentrations related to mechanical stratigraphy. During production through natural pressure depletion, DZEP may dominate well productivity. Under secondary recovery, the same intervals may dominate inter-well fluid flow, causing flood conformance issues, cross-zone fluid movement, bypassed pay, and earlier-than-expected water or gas breakthrough to production wells. Optimisation of production and ultimate recovery relies on collecting the correct kinds of data at a sufficiently early stage in the reservoir characterisation process to permit their inclusion in static and dynamic reservoir models.
Middle Eastern carbonate petroleum reservoirs exhibit a range of heterogeneities which consist of variable combinations of primary stratigraphic and secondary diagenetic and structural characteristics. These produce diverse permeability architectures which can exert a profound influence on reservoir performance during secondary recovery. Of particular importance are laterally persistent discrete zones of elevated permeability (DZEP) that typically make up a volumetrically minor proportion of the reservoir yet show disproportionately high fluid inflow or outflow. The stratigraphic, diagenetic, and structural origins of elevated permeability in Middle Eastern carbonate reservoirs are considered here and the consequences of such features for reservoir performance are discussed. The term DZEP denotes geological sources of elevated permeability at least an order of magnitude greater than background reservoir properties. Stratigraphically organised DZEP comprise coarse-grained layers, event beds or parasequence tops or bases in neritic or platform interior settings. Other origins include bioturbated layers, grainy clinothems, and bed-scale, grain-size variations in shoal deposits. Diagenetic DZEP are typically dissolution horizons with mouldic and touching-vug pore networks or dolomitized intervals which often overprint stratigraphic DZEP. Structural DZEP include individual faults, fracture corridors, and fracture concentrations related to mechanical stratigraphy. During production through natural pressure depletion, DZEP may dominate well productivity. Under secondary recovery, the same intervals may dominate inter-well fluid flow, causing flood conformance issues, cross-zone fluid movement, bypassed pay, and earlier-than-expected water or gas breakthrough to production wells. Optimisation of production and ultimate recovery relies on collecting the correct kinds of data at a sufficiently early stage in the reservoir characterisation process to permit their inclusion in static and dynamic reservoir models.
In recent years, multilateral wells have become more predominant enabling either improved recovery or injectivity depending on the well type. The process of timely accessing the correct lateral with coiled tubing (CT) is still one of the greatest challenges relative to the well intervention. This paper presents a case history in which a flawless 2.375-in CT intervention was performed to stimulate laterals with a proprietary multilateral entry bottom hole assembly (BHA) that steered the CT efficiently into the laterals. The injector well has a natural and un-natural lateral, both of which required stimulation. A proprietary hydraulic multilateral entry tool was selected for the job which reliably locates and enters multiple lateral junctions in a single run. The special working mechanism of the tool circumvents any need for an electrical control or steering system. Along with this tool, a casing collar locator (CCL) was incorporated into the BHA, powered by a proprietary CT conductor telemetry system. Real time data enabled confirmation relative to access into the correct lateral to save time without the need to tag the bottom. A gamma ray (GR) sub can also be incorporated into the BHA to correlate depth where needed. A major challenge for multilateral intervention is time on location. The multilateral entry tool searches for the lateral by rotating 360° until it reaches the desired kick off angle which is confirmed by a surface pressure indication signifying that the correct lateral has been located. The simple yet effective operational mechanism of the multilateral tool allows each lateral to be found and entered in less than 30 minutes once it is positioned at the window. Depth correlation is confirmed with use of either the CCL or GR subs or a combination of the two and the multilateral entry tool is resettable easily by pressurizing, which enables any number of laterals to be located & stimulated. The job was completed safely as per program with more than 4,000 bbl of acid pumped to stimulate both the laterals. The entire operation was conducted efficiently, flawlessly, and post injectivity results of the stimulation resulted in significant incremental injection drainage capability. This combination of BHA's options and the efficient mechanism of the multilateral entry tool to find and enter multiple laterals quickly and reset without the need to pull out of hole, enables the Operator to intervene in any number of branches of a multilateral well in a timely and efficient manner. This is a very important case history for other complex multilateral wells in the region which could benefit from this technology and approach
For a quarter of a century sustained technological advances in multilateral technology have enhanced economics and extended the production life of fields in the Middle East. Multilateral well construction, once considered to be complex, costly and a higher risk when compared to the drilling of a single wellbore, has been widely adopted in the Middle East as a robust, reliable and value adding method of field development or field rejuvenation. Having established confidence in existing multilateral technology and methods, operators in the region have challenged multilateral technology providers to expand and evolve to address more challenging reservoir needs and enable more advanced multilateral wells delivering even greater value. Multilateral applications have evolved in capabilities from simple dual laterals to the addition of allowing intervention capabilities, along with improved junction integrity, and the integration of lateral flow control and monitoring. The use of multilateral technology can deliver a significant increase in reservoir contact compared to single horizontal wells. A dual lateral well can deliver twice the reservoir contact while eliminating the drilling, casing, and cementing of an additional vertical wellbore section. Operators are implementing multilateral field strategies to reduce overall development cost, cycle times, and carbon footprint and providing a new lease of life to existing fields. Further benefits include delivery of wells with more production with less surface facility systems requiring less in-field construction hours and maintenance at a lower baseline cost and risk over the life of the field. This paper discusses the latest multilateral technology developed for operators in the Middle East. It highlights the continuous improvement of multilateral technology used in the region by demonstrating how application of multilateral well strategy is a proven and reliable method to reduce time-intensive operations by eliminating additional vertical wellbore sections and utilizing existing surface infrastructure. Case studies will include discussion of workover intervention operations, completions, infill drilling and lateral creation systems. This paper will focus on how the latest multilateral technology options enable operators in the Middle East to consistently meet challenges and maximize asset value. Wells originally planned as a single wellbore or a simple dual lateral are now drilled and completed using intelligent flow control and, in some cases, installations with pressure-controlled junctions. The paper focuses on a region and the technology used to increase efficiencies, enabling the reliable delivery of increased reservoir contact in less operational days. The paper also provides insights as to the methodology adopted to continually improving reliability of multilateral installations and to maximize efficiencies.
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