Flow Anisotropy Analysis From Multiwell-Testing of Sabiriyah Field, North Kuwait

Abstract

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).