The goal of matrix stimulation of carbonate reservoirs is to improve near wellbore conductivity by generating wormholes and increasing the effective wellbore radius, bypassing damaged areas. In naturally fractured carbonates, the wormholes connect the existing fractures, creates longer flow channels. Most widely used stimulation method in carbonate reservoirs is matrix acidization using HCl with various concentrations. The rapid reaction of HCl with carbonate matrix does not allow the reactive fluid to penetrate deep inside the formation before the acid spends. Therefore, the efficiency of conventional acid is limited, where deep penetration is needed. Stable emulsified acids are found very effective, to combat the challenge. The basic advantages of using emulsified acid are: generates longer wormholes by deep penetration into the formation; better zonal coverage; preferential stimulation of oil zones and less corrosive to workstring and downhole/surface equipment. Based on the extensive laboratory studies, a stable deep-penetrating emulsified acid has been developed for carbonate reservoirs. The formulation is a mixture of HCl with compatible additives, diesel and some suitable emulsifiers. The ratio of the dispersed acid and external diesel phase is maintained as 70:30. Stability of the system is a major concern for adequate retardation and penetration deep inside the reservoir. Stability of emulsion largely depends on reservoir temperature and the HLB number of emulsifier. Two surfactants were identified for the system and the HLB number has been maintained in the range of 5.1–5.2 by optimizing the ratio of two surfactants for achieving the maximum stability. The developed acid system has been applied in some wells of an offshore field of India with encouraging results. The field comprises of naturally fractured limestone formation with number of hydrocarbon bearing sands. This paper describes the development of the Deep Penetrating Emulsified Acid and its application in the field along with treatment methodology and outcomes. Introduction Traditionally, HCl has been used for acidizing carbonate reservoirs as it has high rock dissolving power, does not generate insoluble reaction products, generic in nature and easily available.1, 3 Carbonate acidizing with HCl shows the formation of macroscopic channels, called wormholes. Formation of wormholes is the preferred dissolution process as it establishes good conductivity between reservoir and wellbore. Acid travel inside a pore can be represented by two perpendicular fluxes; a) axial transport by convection and b) transport to the pore walls by diffusion. During injection, the bigger pores accept more acid and it is used to increase the pore length and diameter, which promotes wormhole propagation.1 With low injection rate, all the acid gets consumed in the wellbore face itself, called compact dissolution. Compact dissolution leads to poor stimulation and should be avoided. Therefore, combination of high injection and low diffusion rate is favorable for the growth of denser and longer wormholes. However, the low viscosity and high reactivity of plain HCl often results in poor wellbore coverage and limits the propagation of wormholes. Hence, plain HCl is not always a good choice for stimulating heterogeneous carbonate reservoirs. A stable emulsified acid with controlled diffusion rate of acid towards the rock surface is favorable for the growth of desired wormhole pattern.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe goal of matrix stimulation of carbonate reservoirs is to improve near wellbore conductivity by generating wormholes and increasing the effective wellbore radius, bypassing damaged areas. In naturally fractured carbonates, the wormholes connect the existing fractures, creates longer flow channels. Most widely used stimulation method in carbonate reservoirs is matrix acidization using HCl with various concentrations. The rapid reaction of HCl with carbonate matrix does not allow the reactive fluid to penetrate deep inside the formation before the acid spends.Therefore, the efficiency of conventional acid is limited, where deep penetration is needed. Stable emulsified acids are found very effective, to combat the challenge. The basic advantages of using emulsified acid are: generates longer wormholes by deep penetration into the formation; better zonal coverage; preferential stimulation of oil zones and less corrosive to workstring and downhole/surface equipment. Based on the extensive laboratory studies, a stable deep-penetrating emulsified acid has been developed for carbonate reservoirs. The formulation is a mixture of HCl with compatible additives, diesel and some suitable emulsifiers. The ratio of the dispersed acid and external diesel phase is maintained as 70:30. Stability of the system is a major concern for adequate retardation and penetration deep inside the reservoir. Stability of emulsion largely depends on reservoir temperature and the HLB number of emulsifier. Two surfactants were identified for the system and the HLB number has been maintained in the range of 5.1-5.2 by optimizing the ratio of two surfactants for achieving the maximum stability. The developed acid system has been applied in some wells of an offshore field of India with encouraging results. The field comprises of naturally fractured limestone formation with number of hydrocarbon bearing sands. This paper describes the development of the Deep Penetrating Emulsified Acid and its application in the field along with treatment methodology and outcomes.
This paper describes the development of an integrated production network model for a major producing field located in the Western Offshore Region of India, the second most prolific oil field in India. The purpose is threefold:presentation of a case history describing successful implementation of optimisation methodology in a major gas lifted field,outlining the structure and methodology for constructing and calibrating a large integrated production model, andillustrating the potential applications in running the completed model in optimisation mode. The Heera Field, currently producing from 119 strings (all on gas lift except one) has been on production since 1984 and with recovery in the region of 20% considerable potential still exists for improving production and recovery. One of the areas and challenges for improvement involves the optimisation of the gas lift performance. The Heera network model described in this paper includes the multi-phase well production, gas lift injection, production processing and gas lift compression facilities that comprise the asset. The development of the network model comprised the following elements:Well models were constructed for all the producing strings using nodal analysis. Outflow performance was calibrated to existing flowing gradient survey (FGS) data and recent production test data.Fluid properties were characterized based on Black Oil correlations using four independent PVT datasets, and tuned to a single correlation across the entire field.Approximately 450 independent pipe/flowline objects were included in the model to represent major pipelines, risers and downcomers.Three major processing platforms, comprising 5 HP separators, MP and LP separators, and 5 gas lift compressors operating in parallel were modelled.Production from neighbouring complexes (Neelam and ICP) was included in the form of "object sources" with overall delivery point at the Uran terminal located onshore. The network model was built, history matched and calibrated to actual field data, within a tolerance of <1% for the measured liquids production. The calibrated model was then used to run a number of optimisation scenarios, in an effort to find ways of improving production and operating efficiency. Optimisation investigations conducted within the framework of this project indicate potential oil uplift of between 6–8% from a combination of well interventions (based on individual well modelling and gas lift diagnostics) and network optimisation (lift gas reallocation), as well as a reduction in total lift gas requirement and compressor horsepower. Besides the scope for production gains and operational improvements, the project also highlights a number of higher level issues relevant to the development and employment of integrated production network models:The successful implementation of the Heera network model is the first of its kind in ONGC's India operations.The technology utilised in this project is capable of modelling large scale complex production networks in a robust and reliable manner. Complexity and size need no longer be barriers to successful implementation of network modelling and optimisation.The technology is easily transferable for implementation by production engineering and operations staff in the field, provided standardised workflows are identified and new work practices implemented to allow improved data management and model maintenance.The maintained integrated production network model provides a platform for analysing and diagnosing a wide variety of production and equipment related issues in the field.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThis paper describes the development of an integrated production network model for a major producing field located in the Western Offshore Region of India, the second most prolific oil field in India. SPE 101089Recommendations from the model are currently being implemented in the field. Based on the modelling recommendations, well interventions and lift gas reallocation have so far produced oil production increases in the region of 1700 BOPD.
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