IRANIAN JOURNAL OF PETROLEUM GEOLOGY
Year:2017 | Volume:7 | Issue:13 |Papers Count:6

Many studies have documented that quality of the Asmari Formation, as the main hydrocarbon reservoir rock in Southwest Iran, is often affected by fractures systems. In this study, in order to study fracture patterns in the Asmari Formation, as well as to present a natural analog model for the other Asmari reservoirs, the Dara anticline in South Dezful Embayment, which has extensive outcrops of the Asmari Formation, was considered. During field studies, eleven stations on the anticline, in its different structural positions, have been investigated. Four fracture sets, in the southwestern limb of the anticline and in the northeastern limb of the anticline were identified. Also, in its hinge area of the anticline, three fracture sets were detected. In this study, the relative formation time of the identified fractures, relative to folding, has been diagnosed as before or simultaneously with folding event. Based on the field studies, fractures density in the Dara anticline, the Asmari outcrop, ranges from 11.75 to 2 fractures per meter. Indeed, variation range of the fracture length is 1 to 25 m and most of the fractures have a length of lower than 5 meters. Also, in this study it was found that there is a reverse logarithmic relationship between fracture density and sedimentary layer thickness.

In this research based on petrography study of 320 thin sections (cutting samples), biostratigraphy, microfacies and depositional environment analysis has been done to determine the boundary between the Shahbazan and Asmari formations in well No.1 of the Balarud Oil Field, located in the north of Dezful embayment. The Shahbazan Formation with 460 meters thick with mainly composed of dolomite along with interlayers of limestone, shale and anhydrite in the studied well. The lower boundary of this formation with the Pabdeh Formation is conformable and its upper boundary with the Asmari Formation is marked by an unconformity. The Asmari Formation with thickness of 140 meters mainly consists of limestone and shale with the interlayers of dolomite; its upper boundary to the Gachsaran Formation is conformable. Biostratigraphy studies documented a high diversity of shallow-water benthic and rare planktonic foraminiferas and led to the determining of one assemblage zone in the Shahbazan Formation (15 genera and 8 species) that indicates age of the Priabonain. Three assemblage zones also were recognized in the Asmari Formation (12 genera and 8 species) that, shows the age of the Asmari Formation from Mid-Rupelian to the Chattian, Aquitanian and Burdigalin. Based on biostratigraphy studies, the boundary between Shahbazan and Asmari formations and the position of an unconformity between them were determined. The facies analysis led to recognition of eight microfacies for the Shahbazan Formation which belong to three facies belts of inner (tidal flat and lagoon), middle and outer ramp, deposited on a ramp-type carbonate platform. Also four microfacies were recognized in the Asmari Formation which are related to the inner carbonate platform.

Permeability is one of the most important parameters for characterization of hydrocarbon reservoirs that has a basic role in almost all of the petroleum engineering problems. Determination of reservoir permeability is usually done in core laboratories in a time consuming process. In the well test, the obtained average permeability is related to the drainage area. Due to cost, these two methods are not performed in the all wells, whereas well logging tools are generally performed in all wells.With progress of well logging tools, some researchers tried to estimate permeability from special well logs such as NMR directly. The data obtained from NMR was used as lithology independent data to estimate the water saturation and porosity, and also for analysis of pore space. One of the important parameters obtained from NMR is the transversal relaxation time (T2).In this work, NMR log measurement in zones 1 and 2 of Sarvak Formation was used to estimate the permeability using Timur, SDR and regression models. The results of the methods were compared against core permeability. The results show that SDR method is more accurate with the accuracy of 44.1% and the error of 23.12%.

Nowadays, it is claimed that the best tools and techniques to have geochemical evaluations of source rocks is to utilize Rock-Eval analysis. In this research, for evaluating Geochemical features, of Gurpi and Pabdeh formations in Binak fields, Dorood and Hendijan, Geochemical analysis (preliminary analysis includes Pyrolysis and Rock-Eval) have taken places on 27 samples of drill cuttings. The results of pyrolysis of Rock-Eval illustrated that with analyzing the ' oil immigration indicators' and ' degree of contamination' of samples, in the zones of oil generations were authigenesis which that there is no saturation of minerals with corrosion of samples.The type of corrosion in source rocks of Gurpi and Pabdeh formation in Binak fields is type 2 and 3, and also a compound of these two, which in Dorood fields the tendency is more to the type 3 corrosion (the ability in generating more petroleum).Measuring the amounts of TOC (total organic carbons) of Gurpi and Pabdeh formations in the fields of Binak, depicts that the candidate source rock is weak in minerals and samples of Gurpi formation in the fields of Dorood is rich in minerals and this presents a high degree of maturation (the beginning of oil windows).Samples of Pabdeh formation, in fields of Hendijan holds a high TOC, but mineral maturation stays in the last stages of diagenesis and has not yet entered the stage of ''oil generating window", thus they cannot act as the main source rock of Hydraulic fluids.With all considered, Gurpi formation in most cases (samples) shows petroleum zones and is the greatest potentiality in oil generation and is related to Gurpi formation in Dorood fields which can act like source rocks in charging petroleum Reservoir.The type of the determined organic facies in Gurpi and Pabdeh formation in fields of Binak and Dorood, has conditions of oxidation and semi-revival, and Pabdeh formation in Hendijan shows revival conditions which illustrates marine environments and Intermediate Rocks.

Estimation of petrophysical parameters of hydrocarbon reservoirs such as porosity and permeability using 3D seismic data is considered as an efficient and effective tool for comprehensive study of reservoirs as well as reservoir management. In this study, which was carried out on one of the oil fields in the Persian Gulf, the aim is to simulate the petrophysical parameters of effective porosity and permeability by using Co-Sequential Gaussian Simulation in part of Middle-Sarvak reservoir. With this simulation, a three-dimensional model of petrophysical reservoir parameters can be presented which is important for simulating fluid flow and identifying areas that are prone with higher reservoir quality. For this purpose, effective porosity and permeability logs of seven wells with a 3D seismic cube and seismic inversion results have been used. After reservoir gridding and creating a structural model, up scaled petrophysical data has entered to a model. For three-dimensional distribution of effective porosity parameter, due to the correlation of effective porosity and acoustic impedance attribute of seismic inversion, up scaled effective porosity logs as the initial data and acoustic impedance attribute of seismic inversion as secondary data have entered using Sequential Gaussian Simulation and Co-Kriging techniques. In order to simulate permeability, due to the good relationship between the effective porosity model obtained by simulating and up scaled permeability log, the effective porosity simulated as a secondary data and up scaled permeability log is used as initial data in Sequential Gaussian Simulation and Co-Kriging techniques. The results of validation indicate the accuracy of the present study and the efficiency of the Sequential Gaussian Simulation method in effective porosity and permeability modeling in this reservoir.

The rapid development of shale gas resources in the US has transformed the world gas-market outlook. Despite this, the consensus was for a long time that shale gas would not bea ‘game changer’ in the world as it has been in the US. Shale gas is extracted from solid rock using a process called hydraulic fracturing, or ‘fracking’. Static shows, in USA, production rates decline, for the most of well on average, 80 0r 85 percent over the three years. In order to maintain current level of shale gas production, Hughes estimates that the high rates of deterioration of such wells across the US will require the drilling of 7, 000 new wells a year at cost of $42 billion annually. For the maintenance of overall production of shale oil, some 6, 000 new wells would need to be drilled every year, an endeavor that would cost $35 billion. A number of environmental concerns have been raised about fracking, including the potential for seismic events, air pollution, surface and groundwater contamination, and greenhouse gas emissions. There is no doubt that shale revolution has been a game-changer in short term, but the implication shows that it is not sustainable in long-term.