The Design and Early Performance History of Two Waterflood Pilots in the Mauddud Carbonate Reservoir, North Kuwait
Abstract: This paper was prepared for presentation at the 8th Abu Dhabi International Petroleum Exhibition and Conference held in Abu Dhabi, U.A.E., 11-14 October 1998.
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Middle Eastern carbonate reservoirs – the critical impact of discrete zones of elevated permeability on reservoir performance
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 reservoirs – the critical impact of discrete zones of elevated permeability on reservoir performance
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.
fax 01-972-952-9435. AbstractSabiriyah Mauddud (SA MA), a super giant depletion drive oil reservoir in North Kuwait (NK), is undergoing massive development efforts, with a planned enhancement in oil production through phased pattern waterflood. The Phase1 development covers the crestal area of the structure, which is the focus for current development efforts through 12 inverted 9-spot patterns. This paper outlines the successful integration of subsurface, water handling, well surveillance and production operations teams across the NK asset to significantly improve the operating procedure for waterflooding the SA MA reservoir. This effort required a new way of managing this reservoir in NK: a comprehensive approach of balancing voidage with injection, conducting extensive surveillance/analysis within the reservoir to assess the efficacy of various courses of action and, most significantly, adjusting various teams' "key performance indicators" to align injection and production allowables with sound reservoir management principles.The health of the waterflood is regularly checked and monitored through revision of production/injection allowable and pattern balancing. An innovative unified information management system was used to monitor voidage replacement ratio (VRR) to provide a basis for pattern balancing. A very extensive surveillance operation provides the data necessary to monitor individual pattern balance and watercut performance, optimize areal sweep efficiency by adjusting injection and production allowables, assist in planning water shutoff operations, and design new completions.Time lapsed monitoring and the surveillance data indicates the reservoir is relatively well connected. Pattern VRR, pressures, and watercuts were somewhat out of balance prior to engaging in this effort. However, after applying the new management approach, individual waterflood pattern balance is significantly improved and the field-wide VRR is around 1.2.All of these activities have led to the enhanced understanding of the waterflood behavior and the model updates. Sound reservoir surveillance and waterflood management procedures implemented within a diverse group of teams that have performance goals aligned with "best practice" has resulted in effectively re-balancing this major waterflood. This effective integration of teams retains the flexibility to adjust for an ongoing development of this super giant field. This paper also brings out the case history of waterflood management in a super giant carbonate reservoir and the challenges met during the last seven years since the commissioning of the waterflood in year 2000.
The Sabiriyah field in north Kuwait showed a depletion drive mechanism and a water flooding plan was needed. The Mauddud reservoir was tested through a Waterflood pilot which incorporated a pulse test data. The objective of the test is to assess reservoir connectivity, properties and water flow direction. The field's test data were matched through a pressure distribution with a slight heterogeneous and a homogeneous match. Using the field data, a small range of anisotropy orientation N10oE to N7oE was found. This orientation correlates to the sand fairways in the direction of SW-NE mentioned in the literature. Two cases were used to verify that the first peak of the pulse test can be used in an interference analysis with a decreased value of total compressbility. For all cases, the well's sequence is the same as the original response but the separation between the three well's pressure responses was not as clear as the original data. The Papadopulos-Ramey's method was used to evaluate the two matches of the Sabiriyah's pulse test. The slight heterogeneous match was used and the results were consistence with orientation of N8E and anisotropy ratio of 32. Also, the decreased value of total compressibility in the ideal case was verified using this method. The second homogenous match could not be evaluated because the field had a slight heterogeneity that affected the transmissibility result. Also, the gap in the diffusivity between the three wells is high, which cannot be presented by the anisotropy alone, compared to the three ideal cases. In addition, ideal homogeneous modeled pulse test of the field with orientation of N8oE verified that the gap in diffusivity between the wells cannot be modeled without varying and decreasing the total compressibility value for the three wells. Introduction The Sabiriyah field was discovered in the late 1950's and production commenced in 1958 under Kuwait Oil Company's supervision. The Mauddud reservoir in Sabiriyah field has produced a cumulative of 187 MMbo as of December 2005, which represent a very small percentage of the Original Oil in Place. The Mauddud reservoir consists of a blocky section of Cretaceous limestone, characterized by layers of moderate permeabilities (10–100 mD) with high permeability zones within the main reservoir interval. The overall thickness is 350 to 400 feet. The upper portion of the reservoir is the main pay interval. Fig. 1 is a map showing the location of Sabiriyah field in North Kuwait (Ibrahim et al., 2007). The Mauddud reservoir is overlain by minor carbonate reservoirs viz. Tuba and underlain by Lower/Upper Burgan reservoirs. The reservoir is comprised predominantly of mid ramp packstones. Presence of higher energy grainstones and floatstones typically result in higher permeability layers within the reservoir (Chetri et al., 2005). Table 1 shows the average properties of the Mauddud reservoir. This reservoir is a single phase reservoir because the current pressure is above the bubble point pressure as shown in Table 1. Sabiriyah fluid movement appears to be dominated by the grainstone/packstones interval. Water movement at the Mauddud reservoir appears to be affected strongly by sand fairways SW-NE in central and northern parts of the field. Edge water appears to enter more strongly from the south west, north east and east in central and northern parts of the field (Chetri et al., 2004).
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