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Openhole gravel packing is one of the most popular completion techniques, due to its high reliability along with the ability to deliver high-productivity wells. Currently, there are two techniques used for gravel placement, one utilizing low-viscosity carrier fluids and low gravel concentration. In this technique the gravel is placed in two waves commonly called Alpha/Beta packing. The second method utilizes a viscous carrier fluid and high concentrations of gravel in conjunction with alternative path screens which mitigate problems caused by unpredicted downhole events. In this paper we present a new approach for gravel packing long high angle openhole intervals without the need for alternative flow path screens but retaining the advantages of high gravel concentration slurries. This is supported by 2 field case histories from a field in India, where two gas wells were drilled with an oil-based drill-in fluid and gravel packed with a viscous water-based fluid. The packing mechanisms and efficiencies in these applications have been verified with downhole gauge analysis as well as mass balance calculations. Both wells are producing sand free with hydrocarbon production that met or exceeded operator expectations, with zero mechanical and extremely low rate dependent skins. Introduction Openhole gravel packing is one of the most popular completion techniques, particularly in deepwater developments with high transmissibility, due to its ability to deliver reliable, high productivity wells.1,2 Current techniques used for gravel packing horizontal wells include Alpha/Beta,3 Alpha/Alpha4 and Alternate Path packing.5 The first two techniques use a low viscosity carrier fluid (typically brine) with a low gravel concentration (typically 1.0 ppa). In both techniques, initial packing takes place in the lower part of the horizontal well until the bottom is packed all the way to the toe (called the Alpha Wave), if circulation can be maintained. This part is dominated by settling of the gravel up to an equilibrium height which is controlled by the circulation rate, with higher rates leading to lower bed heights. In the Alpha/Beta technique, the circulation rate is kept constant, and the packing proceeds from toe-to-heel, covering the upper part of the horizontal well (called the Beta Wave), once the Alpha Wave reaches the toe. For typical Alpha Wave height designs used in these treatments (barely covering the screens), pressure increase during the Alpha Wave is negligible, although the pressure rise during Beta Wave can be substantial. This is because of the narrow annulus between the screen base pipe and the wash pipe, through which the carrier fluid must travel and reach to the entry point into the wash pipe for returns to surface. Such pressure rise can be problematic in cases where the operating window between downhole circulation pressure and the fracturing pressure is narrow. Various hardware and chemistry solutions exist to overcome this problem, including diverter valves that are activated sequentially creating a new entry point upstream into the wash pipe,6 light weight gravel which allows lower pump rates for the same alpha-wave dune height as in conventional gravel7 and drag reducing additives that can be used in the carrier fluid either throughout the treatment or during the Beta Wave.8
Openhole gravel packing is one of the most popular completion techniques, due to its high reliability along with the ability to deliver high-productivity wells. Currently, there are two techniques used for gravel placement, one utilizing low-viscosity carrier fluids and low gravel concentration. In this technique the gravel is placed in two waves commonly called Alpha/Beta packing. The second method utilizes a viscous carrier fluid and high concentrations of gravel in conjunction with alternative path screens which mitigate problems caused by unpredicted downhole events. In this paper we present a new approach for gravel packing long high angle openhole intervals without the need for alternative flow path screens but retaining the advantages of high gravel concentration slurries. This is supported by 2 field case histories from a field in India, where two gas wells were drilled with an oil-based drill-in fluid and gravel packed with a viscous water-based fluid. The packing mechanisms and efficiencies in these applications have been verified with downhole gauge analysis as well as mass balance calculations. Both wells are producing sand free with hydrocarbon production that met or exceeded operator expectations, with zero mechanical and extremely low rate dependent skins. Introduction Openhole gravel packing is one of the most popular completion techniques, particularly in deepwater developments with high transmissibility, due to its ability to deliver reliable, high productivity wells.1,2 Current techniques used for gravel packing horizontal wells include Alpha/Beta,3 Alpha/Alpha4 and Alternate Path packing.5 The first two techniques use a low viscosity carrier fluid (typically brine) with a low gravel concentration (typically 1.0 ppa). In both techniques, initial packing takes place in the lower part of the horizontal well until the bottom is packed all the way to the toe (called the Alpha Wave), if circulation can be maintained. This part is dominated by settling of the gravel up to an equilibrium height which is controlled by the circulation rate, with higher rates leading to lower bed heights. In the Alpha/Beta technique, the circulation rate is kept constant, and the packing proceeds from toe-to-heel, covering the upper part of the horizontal well (called the Beta Wave), once the Alpha Wave reaches the toe. For typical Alpha Wave height designs used in these treatments (barely covering the screens), pressure increase during the Alpha Wave is negligible, although the pressure rise during Beta Wave can be substantial. This is because of the narrow annulus between the screen base pipe and the wash pipe, through which the carrier fluid must travel and reach to the entry point into the wash pipe for returns to surface. Such pressure rise can be problematic in cases where the operating window between downhole circulation pressure and the fracturing pressure is narrow. Various hardware and chemistry solutions exist to overcome this problem, including diverter valves that are activated sequentially creating a new entry point upstream into the wash pipe,6 light weight gravel which allows lower pump rates for the same alpha-wave dune height as in conventional gravel7 and drag reducing additives that can be used in the carrier fluid either throughout the treatment or during the Beta Wave.8
In the early days of the oilfield, matrix acidizing was considered useful only for stimulating carbonate formations. However it has been known for many years that with proper job design, acid and additive choices, and in-depth study of potential formation damage sources, matrix acidizing can safely and successfully stimulate production in sandstone formations. By incorporating carefully designed tubing pickle, pre-flush, main acid system and post-flush (including optimum doses of corrosion inhibitors, mutual solvents, iron control agents, clay control additives, surfactants, etc.), matrix acidizing can provide excellent productivity improvements even in sandstone formations with complex mineralogy. This paper describes a matrix acidizing campaign executed successfully in the Gulf of Cambay (Khambhat) on the west coast of India. In initial laboratory tests and during simulation runs, it was aimed to design a pre-flush, acid system and post-flush to best suit the challenging reservoir conditions while also considering offshore logistics. Further as the formation had iron-rich minerals like chlorite clay, siderite, etc., a chemically modified organic sandstone acid system was selected as opposed to conventional hydrofluoric acid system. Moreover a spacer system was designed and pumped to push any iron precipitation far away from the near-wellbore area and to clean the area for the organic acid system. After pumping the system in one well, the system design, pumping procedures and volumes were modified to further improve results in the next well. Fines-stabilizing agents were introduced to avoid clay migration or swelling that may otherwise jeopardize a successful treatment. The paper will explain the basis for modifying the design and pumping procedure, based on lessons learned from the prior operation.
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