The use of borehole image interpretation in characterising cement nodules and associated nodule-bound micro-fracture distribution in the Mauddud Formation, North Kuwait
Nick Foote, Daniel Clay and Meriem Bertouche
The Lower Cretaceous Mauddud Formation in North Kuwait is a limestone-dominated transgressive-regressive sequence of about 380ft (116m) thick. As a key reservoir in North Kuwait, it has been extensively studied with permeability heterogeneity caused by diagenesis a concern for production. How cement is distributed through the reservoir from nodules to cement cycle tops, together with how fractures interact with the cements, has been the focus of previous studies (Dewever et al., 2020). However, minor variations in wireline log response across the carbonate succession makes extrapolating nodule distribution from cored to uncored intervals challenging with fractures undeterminable altogether. This study utilises BHI across 50 wells to characterise nodules and cements where core is absent to better understand these heterogeneities. This can be used to support the reservoir connectivity understanding and facilitate full field development planning.
Although largely unable to describe depositional texture of the carbonates, the extensive borehole image dataset has allowed characterisation of the uncored Mauddud in terms of its diagenetic overprint. A robust core-calibrated descriptive scheme captures nodule size, density and cement banding which are clearly differentiated from interbedded clastic intervals. This has enabled confident mapping of cement distribution within specific reservoir zones and the identification of cycles comprising upward-coarsening of nodules that may have a link to regressive cycles of varying orders therefore assisting in determining sequence stratigraphic interpretations.
Nodule-bound micro-fractures are key for increasing permeability in heavily cemented intervals. These micro-fractures have been identified in the image with varying degrees of certainty due to image quality variations and varying contrast with the host nodule. The vertical distribution of these have then been documented and fracture frequency mapped for each reservoir zone.
Foote, N, Clay, D, Bertouche, M, El-Aziz, S, Chen, C, Ramalingam, R, Boland, G and Helmy, M. (2022) The use of borehole image interpretation in characterising cement nodules and associated nodule-bound micro-fracture distribution in the Mauddud Formation, North Kuwait Paper presented at the AAPG Carbonate Sequences and Reservoirs Conference, Naples, 22-23rd Jun, 2022.
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The use of borehole image interpretation in characterising cement nodules and associated nodule-bound micro-fracture distribution in the Mauddud Formation, North KuwaitDownload PDF (3.80mb)