Abstract
Karachaganak Field is an isolated carbonate bank consisting of Carboniferous to Lower Permian carbonate deposits located in the northern margin of the Pre-Caspian Basin of Kazakhstan. Discovered in 1979, it represents one of the largest gas and condensate reservoirs in the world and has been in production since 1985. This paper focuses on the different modeling methods applied to Late Visean sequence to try to improve the reservoir model reliability. In fact although this interval is relatively thin, it is mostly located inside the Oil Rim interval, so that it strongly impacts the present development phase which is focused on maximizing liquid recovery. This peculiar stratigraphic interval represents the highstand section of the Late Visean sequence and records the initial settling of micro-biohermal deposits constituted by in situ bryozoans, microbial boundstone, cementstone, all facies interlayered with crinoidal limestones. Due to its reduced thickness, there is a minimal contribution of the seismic sequence stratigraphy interpretation to understand the internal structure and geometry of this sequence. Despite its complexity, the Late Visean was initially modeled as a unique "undifferentiated body" characterised by the whole petrophysical data without discriminating the different depositional facies. Now, thanks to new core and analogue data, there is enough information to attempt to model this stratigraphic interval with a more detailed approach, trying to both reconstruct the 3D Facies distribution and utilize the relevant Reservoir Properties. Therefore two additional simulation methods have been tested: Object-Based Modeling and Multiple-Point Statistics Facies Modeling. Thanks to the long historical production, all these alternative scenarios have been compared to the initial SGS approach using the HM as benchmark to evaluate the best methodology to be applied.
