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To meet rising global demands for energy, the oil and gas industry continuously strives to develop innovative oilfield technologies. A large portion of the world's oil and gas reserves are trapped in carbonate reservoirs, particularly in the Middle East. Well stimulation treatments for these highly heterogeneous formations have traditionally relied upon the use of strong mineral acids, e.g. hydrochloric acid (HCl). However, fast rock/acid reaction rates and corrosion issues pose a significant challenge to the longevity and practical application of such treatments. Alternative approaches have been proposed to slow down this process, among the most popular being emulsified acids. In this case, the release mechanism of live acid is governed by droplet contact with the surface of the formation in conjunction with suitable downhole conditions (i.e., temperature, pressure, pH). Upon release, the acid proceeds to rapidly react with the carbonate formation thereby unveiling a conductive wormhole network. This paper presents a systematic experimental study targeting deeper well stimulation using an improved emulsified acid system. The current study demonstrates the success of an emulsion-based system that is stable at elevated temperatures (e.g. up to 300°F/150°C) for a prolonged period of time. To gain a deeper understanding of the dissolution behavior and resultant wormhole morphology, a systematic coreflood study was conducted to identify key parameters that influence the overall performance of the newly developed stabilized emulsified acid. The parameters investigated include: (1) pore pressure, i.e. up to 7,000 psi, (2) flow rate, i.e. up to 5 cm3/min, (3) acid-rock contact time, and (4) fluid treatment composition. Indeed, the stabilized emulsified acid exhibited superior performance as confirmed from coreflood experiments performed at 3,000 psi and 300°F. In this study, 0.65 PV of fluid was injected into a 12″ core and shut-in for a period of 15h, thus giving the emulsion ample time to break in all cases. Interestingly, a 3-fold enhancement in carbonate permeability was observed for the stabilized emulsified acid as compared to the conventional acid-in-diesel emulsion. Moreover, the CT images for the treated core samples show that the stabilized acid system had less face dissolution and had the desired wormhole characteristics, i.e. narrow and directional propagation behavior with deeper penetration into the core sample. Finally, additives were defined and used to improve the performance of emulsified acid systems at high temperature, which in turn improved the acid penetration rate and wormhole propagation.
To meet rising global demands for energy, the oil and gas industry continuously strives to develop innovative oilfield technologies. A large portion of the world's oil and gas reserves are trapped in carbonate reservoirs, particularly in the Middle East. Well stimulation treatments for these highly heterogeneous formations have traditionally relied upon the use of strong mineral acids, e.g. hydrochloric acid (HCl). However, fast rock/acid reaction rates and corrosion issues pose a significant challenge to the longevity and practical application of such treatments. Alternative approaches have been proposed to slow down this process, among the most popular being emulsified acids. In this case, the release mechanism of live acid is governed by droplet contact with the surface of the formation in conjunction with suitable downhole conditions (i.e., temperature, pressure, pH). Upon release, the acid proceeds to rapidly react with the carbonate formation thereby unveiling a conductive wormhole network. This paper presents a systematic experimental study targeting deeper well stimulation using an improved emulsified acid system. The current study demonstrates the success of an emulsion-based system that is stable at elevated temperatures (e.g. up to 300°F/150°C) for a prolonged period of time. To gain a deeper understanding of the dissolution behavior and resultant wormhole morphology, a systematic coreflood study was conducted to identify key parameters that influence the overall performance of the newly developed stabilized emulsified acid. The parameters investigated include: (1) pore pressure, i.e. up to 7,000 psi, (2) flow rate, i.e. up to 5 cm3/min, (3) acid-rock contact time, and (4) fluid treatment composition. Indeed, the stabilized emulsified acid exhibited superior performance as confirmed from coreflood experiments performed at 3,000 psi and 300°F. In this study, 0.65 PV of fluid was injected into a 12″ core and shut-in for a period of 15h, thus giving the emulsion ample time to break in all cases. Interestingly, a 3-fold enhancement in carbonate permeability was observed for the stabilized emulsified acid as compared to the conventional acid-in-diesel emulsion. Moreover, the CT images for the treated core samples show that the stabilized acid system had less face dissolution and had the desired wormhole characteristics, i.e. narrow and directional propagation behavior with deeper penetration into the core sample. Finally, additives were defined and used to improve the performance of emulsified acid systems at high temperature, which in turn improved the acid penetration rate and wormhole propagation.
Azimuthal acoustic logging-while-drilling (LWD) sensors have recently been used in a bottomhole assembly (BHA) to evaluate the viability of sourceless formation evaluation compared to conventional density-neutron data acquired in the same run in a horizontal well across a carbonate sequence. Borehole deterioration and significant pore pressure variations across the reservoir layers pose wellbore stability risks during the drilling phase, which has historically requireddrilling deviated pilot-hole sections for evaluation purposes. These sections were then plugged, backed, and sidetracked. Previous experiences in the same geological setting also encountered extreme borehole enlargements. LWD helped acquire high-quality data before borehole enlargement occurred. Additionally, possible rock anisotropy indications were observed, and rock mechanical moduli were derived. The results were then correlated and normalized to existing field geomechanics knowledge and offset well data. Azimuthal acoustic tools, free of radioactive sources, were run in an LWD tool combination, with the primary objective of measuring porosity, pressure prediction, and possible anisotropy using a four-axis acoustic caliper sensor. This paper discusses the planning, design, and execution of an LWD azimuthal acoustic tool in the case study well. Additionally, the viability, integrity, and robustness of logged data as well as interpreted results are discussed. Optimization of real-time drilling operations and petrophysical dataacquisition requirements are also investigated to help optimize future field development data-acquisition requirements and overall reservoirmanagement strategies.
Proppant fracturing treatments in sandstone formations are routinely executed in Kuwait, however when carbonate formations are the target, acid fracturing is the preferred treatment method. It has been observed that acid fracturing delivers a high initial production however maintaining a sustainable production rate is a challenge in the tight cretaceous carbonate formations in Kuwait. A production enhancement technique needed to be identified in order to deliver more sustainable production and maximize recovery from these carbonate formations. Based on global experience it was proposed that proppant fracturing can deliver more sustainable production rate as compared to acid fracturing. Proppant fracturing had been previously attempted on two occasions in Kuwait, however both the attempts were evaluated as not being operationally successful. Hence prior to executing the first successful proppant fracturing treatment in carbonates in Kuwait a thorough study was undertaken to identify and mitigate the possible risks. The cretaceous carbonate formations in North Kuwait are relatively shallow and are known to be tight and highly ductile. Due to the ductility of these formations, proppant placement and reduction of the fracture conductivity due proppant embedment were thought to be significant risks. During the course of the project, detailed core analysis and testing was conducted using formation core samples to ascertain the severity of this risk. Successful execution of this hydraulic fracturing treatment was pivotal in order to plan the future production strategies from these formations. A cautious approach needed to be followed as proppant placement was of paramount importance. Different strategies were incorporated in the fracturing workflow to ensure the success of the treatment and to maximize data collection in order to optimize future treatments and well placement. Multiple mini-fracs, temperature logs and pumping of novel non-radioactive tracer proppant were some of the techniques utilized. During execution various decisions were taken real-time to ensure success of the treatment. It was observed that all parameters were consistent with the results of the core and laboratory testing conducted during the initial phase of the project which lead to optimizing the proppant placement. The success of this treatment has been a game changer resulting in more wells being identified as candidates for proppant fracturing in this field. Now that proppant placement has been established the objective of future treatments is to optimize fracture designs, fluids and treatment schedules which will help the future production enhancement strategy for this field. Lessons learnt from this first successful well will be applied to future wells planned in carbonate reservoirs in Kuwait, in order to maximize recovery.
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