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Farrokhrouz M.,NIOC | Asef M.R.,Kharazmi University
EAGE Shale Workshop 2010: Shale - Resource and Challenge | Year: 2010

Shale instability is essentially driven by changes in stress and/or chemical alteration. However, sometimes less attention may be paid to geochemical processes. In addition, some well engineering approaches may inevitably facilitate geochemical alterations. An appropriate decision may be more difficult if shale is observed as interbred layers in a carbonate reservoir (rather than as a cap rock). In this research an exceptional approach was chosen to identify geochemical processes that induced geomechanical instability in a gas reservoir with shale interbeds in the South of Iran. Nevertheless, the problem and potential solutions were worked out corresponding to the conceptual engineering geological skills. The results showed that excessive water and HCL acid (traditionally used for well stimulation) in contact with shale interbeds could have significantly contributed in plugging of the well. Site investigations revealed that the amount of excessive (unwanted) water, to a large extent depends on the gas production rate. A systematic analysis of geochemical processes at different production rates was conducted. Mineral precipitation/dissolution of shale formation was simulated accordingly. Corresponding geomechanical interpretations were considered as key points to make an appropriate decision based on economic production rate and the likely well engineering problems.

Rashidi M.,NIOC Exploration | Jalai M.,NIOC | Seragi H.,Padyab Tajhiz
1st EAGE Basin and Petroleum Systems Modeling Workshop: Advances in Basin and Petroleum Systems Modeling in Risk and Resource Assessment | Year: 2014

The integrated Petroleum Systems Modeling Study was carried out with the software PetroMod, with the main aim to determine prediction and reconstruction of the thermal history, hydrocarbon generation and source rock maturity over geological time, exploration prospect ranking for future exploration strategy in the Central Iranian Sedimentary Basin. The structural evolution, which is partly complex involving salt movement and inverse faulting, has been reconstructed. Detachment folding in Alborz and Sarajeh during Miocene has led to hydrocarbon reservoirs since the end of Miocene. These were accumulated in the paleo-anticlines. The target ranking shows that the essential risk in the CIB is the sealing risk. Optimistic constructed scenarios, interpreted with a shale sealing lithology at the base of the URF (sealing the top of Qom Formation), show hydrocarbon charges in the reservoirs at the top of Qom Formation. The target ranking is based on realistic petroleum charge scenarios with a combination of different sealing features was carried. Finally petroleum system outputs used to reconstruction of Sarajeh gas field in Gas injection project and condition of reservoir for type of gas will be injected.

Yarmohammad Tooski Z.,NIOC
73rd European Association of Geoscientists and Engineers Conference and Exhibition 2011: Unconventional Resources and the Role of Technology. Incorporating SPE EUROPEC 2011 | Year: 2011

NMR logs use nuclear magnetic resonance to estimate high resolution total porosity, free-fluid volume, bound-fluid volume and permeability. In this study twomethodologies to generate synthetic CMR logs are presented. In this approach ANN is used as the main tool. Neural network model is developed using CMR logs and conventional logs such as gamma ray, neutron, resistivity and etc. obtained from three wells of South Pars Field, Iran. Then the model is applied to generate synthetic MRI logs such as Free Fluid porosity (CMFF), Bound Fluid porosity (BFV) and permeability (KTIM) by using just the conventional logs in another well. The Synthetic logs are generated through two different methods of Backpropagationand Generalregression. The results presented that MRI log can be generated with a high degree of accuracy. And thebest performance was obtained for Generalregression architecture with approximately 93%-98% accuracy. By using this method the synthetic MR logs can be predict for all the wells in the field and a much better reservoir characterization can be achieved at a much lower cost. Also Generalregression is a more powerful method to generate synthetic logs compared to Backpropagation especially in case of lack of the data.

Farrokhrouz M.,NIOC | Asef M.R.,Kharazmi University
Deep Gas Conference and Exhibition 2010, DGAS 2010 | Year: 2010

Dalan and Kangan formations are the most important host gas reservoirs in Iran. These geological formations are extended to other regions, and they are famous as Khuff formation in the Middle East. They are mainly composed of limestone and dolomite with some inter-beds of shale. So far many reservoirs in Iran are hosted by Asmari carbonate formation. However, acidizing in other hydrocarbon formations (Asmari formation) is accomplished similarly. Conventional acidizing operations were performed on Dalan and Kangan formations in one of the gas fields in south of Iran. Substantial reduction of produced gas was observed over a short period of time. For this reason a comprehensive engineering geological site investigation was accomplished to explain the symptoms and avoid possible further deterioration. Connate water samples from the well while production, showed some unexpected results. Different chokes were tested to see if the amount of impurities in the sample would change. To reduce the amount of water accompanied with produced gas, a different choke was selected; but the result was not satisfactory enough based on refinery report. Therefore, the geological features of the well were gathered based on well sketch and logging data. The phase equilibrium of the reservoir rock before and after acidizing was simulated using a software. The results of chemical lab were analyzed to check the kind of the salts in the well. Laboratory chemical experiments were accomplished to explore produced salts in the well. Further investigation revealed that the choke size was not suitable, and inappropriate acidizing could deteriorate the situation. Based on this research, a number of recommendations were suggested to improve the circumstances of production rate. The authors suggested more carefully designed techniques of acidizing to be applied. The results of this research may be used to prevent geomechanical destabilization around the wellbore in similar cases. Copyright 2010, Society of Petroleum Engineers.

Sadri M.,Amirkabir University of Technology | Jamali J.,NIOC
72nd European Association of Geoscientists and Engineers Conference and Exhibition 2010: A New Spring for Geoscience. Incorporating SPE EUROPEC 2010 | Year: 2010

An offset VSP survey was carried out in an oil field in southwest of Iran. A three-component tool with four receiver shuttles spaced at 15 m was used to record the VSP data. Offset VSP surveying closed to the 2D seismic lines was interested to estimate Thomsens (1986) anisotropy parameters and improve processing results. Both surface seismic data and VSP records were engaged in the analysing. For this purpose, a synthetic layered model consisting of several layers with vertical velocity gradients and anisotropy parameters assumed and anisotropic raytracing was performed through the model. Residual times between observed and calculated traveltimes computed and corrected on the depth-velocity model between shot and well position. The combination results obtained from this approach implies the weak anisotropy condition and anisotropy parameters varied between the range of 0.02-0.15. The application of anisotropy parameters in processing stages shows the improvement of NMO correction. © 2010, European Association of Geoscientists and Engineers.

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