Exploration drilling in the Samgori-Patardzeuli area started in 1974 for the Lower Eocene – Paleocene formations, during the exploration campaign oil discoveries were made in Middle Eocene sediments. The Samgori-Patardzeuli Middle Eocene delivered the bulk of the production in Georgia and is now a depeleted reservoir. Although more than 200 well have been drilled up to date, only 13 wells from them were drilled to the Lower Eocene, therefore Lower Eocene have not been studied sufficiently and gas reserves have not been estimated. Despite this, 29.97 million m3 of gas has been prodused so far from the Lower Eocene sediments. This paper describes the successful experience of drilling one of the deepest exploration well PAT-E1 on the Patardzeuli field to evaluate Lower Eocene gas reservoirs. Exploration drilling for oil and gas involves numerous risks related with limited information about geological structure and drilling conditions. Successful drilling of planned deep exploration well requires good understanding of hole stability to find the optimal mud properties, proper casing seat selection and out-of-the-box engineering solutions to reach well objectives. Multidisciplinary team, including drilling engineers, reservoir engineer, geologist, geomechanicist, petrophysicist, drilling engineer, mud engineer worked in collaboration to design and drill one of the deepest exploration well in the area. Interval from surface till Upper Eocene was characterized by offset wells, but most of decisions were made based on trial and error. Main problems in the upper sections were related with extreme borehole breakouts and severe losses, while the lower sections was known for losses and gas kick. The PAT-E1 well was successfully drilled to the main target in the Lower Eocene and penetrated down to the top of Upper Cretaceous formation with well TD at 5020 m. Elimination one of intermediate sections allows to decrease well construction time and costs with controlled risks of borehole breakouts and losses. Geological support allowed to place casing shoes in a very narrow safe interval to separate the interval of high breakout risk and total loss interval of fractured reservoir with abnormally low pore pressure. Real time pore pressure and fracture pressure prediction service in the lower sections allowed to monitor hole condition in real time and provided timely recommendations for well control. The PAT-E1 well is first deep exploration well that was sucsesfully drilled Upper Cretaceous formation on Patardzeuli field which allow to complete advanced formation evaluation and testing. Best practices developed while drilling this well will be applied for future safe drilling in the region.
Fractures are common features of many carbonate reservoirs. Given complex flow network that they create, characterization of dynamic behavior of these reservoirs is often complicated and becomes important, especially, if fractures provide primary pathways of fluid flow. In this paper a novel semianalytical simulator was used to understand the pressure behavior of naturally fractured reservoir containing a network of discrete and/or connected finite and infinite-conductivity fractures. In this study an integrated interpretation methodology is applied to analyze well test data acquired in open hole section of exploration well drilled into highly fractured carbonate reservoir of Lower Eocene - Upper Cretaceous sediments on Patardzeuli field of Block XI-B, Republic of Georgia. The main steps consisted of explicitly modeling fractures - both wellbore-intersecting fractures and fractures located away from wellbore - using formation microimager data and calibrating the model to actual well test response using a unique novel mesh-free semi-analytical simulator designed for fractured reservoirs. Study presents the results of well test of one zone performed in highly fractured carbonate reservoir drilled in Patardzeuli field. The pressure-transient response confirmed the complexity of reservoir and dominant contribution to flow regimes from fractures. It is shown in this paper that there are many factors that dominate transient behavior of a well intersected by natural fractures, such as fracture conductivity, length, intensity and distribution, as well as whether fractures intersect the wellbore or not. Moreover, it was demonstrated that presence or absence of damage on wellbore-intersecting fractures in vicinity of wellbore will impact the pressure- transient behavior of reservoir and shape overall productivity of the well. The novelty of the approach is the analysis of the dynamic behavior using a unique semi-analytical pressure transient simulator for fractured reservoirs. The simulator can be used to obtain a response for arbitrarily distributed infinite and/or finite conductivity natural fractures within the reservoir by modeling them explicitly. In this study, it allowed to maximize the value of well tests by assessing the effect of fractures on reservoir dynamic behavior and obtain matrix and fracture parameters where conventional well test interpretation tools would be deemed unviable.
Fractures are common features of many carbonate reservoirs. Given complex flow network that they create, characterization of dynamic behavior of these reservoirs is often complicated and becomes important, especially, if fractures provide primary pathways of fluid flow. In this paper a novel semi-analytical simulator was used to understand the pressure behavior of naturally fractured reservoir containing a network of discrete and/or connected finite and infinite-conductivity fractures. In this study an integrated interpretation methodology is applied to analyze well test data acquired in open hole section of exploration well drilled into highly fractured carbonate reservoir of Lower Eocene – Upper Cretaceous sediments on Patardzeuli field of Block XI-B, Republic of Georgia. The main steps consisted of explicitly modeling fractures - both wellbore-intersecting fractures and fractures located away from wellbore - using formation microimager data and calibrating the model to actual well test response using a unique novel mesh-free semi-analytical simulator designed for fractured reservoirs. Study presents the results of well test of one zone performed in highly fractured carbonate reservoir drilled in Patardzeuli field. The pressure-transient response confirmed the complexity of reservoir and dominant contribution to flow regimes from fractures. It is shown in this paper that there are many factors that dominate transient behavior of a well intersected by natural fractures, such as fracture conductivity, length, intensity and distribution, as well as whether fractures intersect the wellbore or not. Moreover, it was demonstrated that presence or absence of damage on wellbore-intersecting fractures in vicinity of wellbore will impact the pressure-transient behavior of reservoir and shape overall productivity of the well. The novelty of the approach is the analysis of the dynamic behavior using a unique semi-analytical pressure transient simulator for fractured reservoirs. The simulator can be used to obtain a response for arbitrarily distributed infinite and/or finite conductivity natural fractures within the reservoir by modeling them explicitly. In this study, it allowed to maximize the value of well tests by assessing the effect of fractures on reservoir dynamic behavior and obtain matrix and fracture parameters where conventional well test interpretation tools would be deemed unviable.
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