The current work is intended to show the application of a multiple realization approach to produce a strategic development plan for one of the mines in Karaganda coal basin. The presented workflow suggests using a comprehensive reservoir simulator for a history matching process of a coal pillars on a detailed 3D grid and application of sensitivity and uncertainty analyses to produce probabilistic forecast. The suggested workflow significantly differs from the standard approaches previously implemented in the Karaganda Basin. First, a dynamic model has been constructed based on integrated algorithm of petrophysical interpretation and full cycle of geological modeling. Secondly, for the first time in the region, dynamic modeling has been performed via a combination of history matching to the observed degassing data and multiple realization uncertainty analysis. Thirdly, the described model parameters with defined range of uncertainty has been incorporated into the forecasting of degassing efficiency in the mine using different well completion technology. From the hydrodynamic modeling point of view, the coal seam gas (CSG) reservoir is presented as a dual porosity medium: a coal matrix containing adsorbed gas and a network of natural fractures (cleats), which are initially saturated with water. This approach has allowed the proper description of dynamic processes occurring in CSG reservoirs. The gas production from a coal is subject to gas diffusion in coal micropores, the degree of fracture intensity and fracture permeability. By tuning these parameters within reasonable ranges, we have been able to history match our model to the observed data. Moreover, application of an uncertainty analysis has resulted in a range of output parameters (P10, P50, and P90) that were historically observed. Performed full cycle of CSG dynamic modelling including history matching, sensitivity, and uncertainty analyses has been performed to create a robust model with the predictive power. Based on the obtained results, different optimization technologies have been simulated for fast and efficient degassing through a multiple realization probabilistic approach. The coal reservoir presented in this work is characterized by very low effective permeability and final degassing efficiency depends on well-reservoir contact surface. The decrease of the well spacing led to a proportional increase of gas recovery which is very similar to unconventional reservoirs. Therefore, vertical and horizontal wells with hydraulic fractures have been concluded the most efficient way to develop coal seams with low effective permeability in a secondary medium.
For accurate coal bed methane (CBM) reserves estimation, it is necessary to evaluate reservoir characteristics. We present a workflow for formation evaluation of coalbed-methane wells, by interpretation of a limited number of legacy logs, including data preprocessing, lithology identification, proximate analysis and estimation of gas content of coal beds. This workflow allowed the estimation of ash content from the available logs, including selective log (analogue of photoelectric absorption), which was recorded only on the territory of the former Soviet Union and never used for such calculations before. Even though the logs were recorded by old tools with low vertical resolution, we were able to identify heterogeneity of coal seams, using the principle of core ash content distribution. Integrated analysis of old core data and recent laboratory measurements of samples from coal pillars allowed to calculate proximate properties of the coal, which showed good match with observed data and could be considered as input parameters for property distribution in the geological model. Also, it is worth to mention that an advanced plug-in was deployed to perform calculation of proximate properties and gas content for all available options and to significantly reduce time for screening different algorithms and rapidly analyzing results.
The Bulak field is a unique oil field located in the South-Turgai basin. It consists of heterogeneous carbonates. Throughout the field, the reservoirs vary from highly fractured clean limestones with strong aquifer to very tight limy claystone with low amount of bed-bound fractures and no water production. Active infill drilling followed after the exploration stage revealed uncertainties related to the main issues of development, i.e., location of new wells, their trajectory, EOR techniques and most importantly, waterflooding. A comprehensive study was conducted based on all the petrophysical, seismic, geological, and reservoir engineering data. As a result, 3D geological and dynamic models were built. During the analysis, special focus was on geological structure and petrophysical characteristics as well as pressure transient analysis due to drastic changes in reservoir properties within small distances. In addition, the production history and the main stimulation, and EOR measurements, especially fracturing, acidizing and nitrogen huff ‘n’ puff results, were taken into account. Eventually, the waterflooding was simulated to identify its benefits and possible field application. Based on comprehensive study, the field is divided into several zones. The main criteria for dividing became a lithology that is represented by weathered crust, pure limestones, shaly limestones, limy claystones, and bioliths. Each part requires a different approach in development. If the north part is highly fractured and consists of limestones, water shut off is required due to active aquifer, middle part pressure support and the south part horizontal drilling or sidetracking with multistage high-tonnage fracturing. As a result, waterflooding was decided to be implemented in the part of the field characterized by ultralow permeability formation. Thus, recently, four producers were converted to water injection along with the fact that the injection is performed using low-salinity water. Surprisingly, injectors' rates are high enough, current voidage replacement ratio is sufficient and the results are unexpected. The reservoir is very complex where the lithology is drastically distributed within a small area. However, most of the territory is represented by very tight formation. Eventually, after several years of fields operation, many aspects became clear after the research work and development strategy was updated. So, the company is ready to develop such an unconventional reservoir that is one of the few fields in Kazakhstan.
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