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Sand, or fines as some may call it, entering currently producing wells is one of the earliest problems faced by the Oil and Gas Industry in hydrocarbon recovery [Rogers, 1954; Carlson et al. 1992; McLeod 1994; JPT Staff 1995; Barrilleaux et al. 1996], and one of the toughest to solve in general [McLeod 1997]. Every year the petroleum industry spends significant capitol in cleaning and disposal costs, repair problems related to sand production, and lost revenues due to lower production rates due to mitigation efforts [Mathis 2003; Palmer et al. 2003]. Thus, sand control is, and should be, an integral part of well planning [Guerrero 2014] in unconsolidated reservoirs [Willson et al 2002; Chang 2006; Jaimes 2012], i.e., reservoirs where the rock has little or no natural inter-grain cementation. Sand production [Veeken et al. 1991; Subbiah et al. 2021] is caused by structural failure of the borehole wall rock due to drilling, degree of consolidation (very low compressive strength), the interaction between the rock and flowing fluids (production creates pressure differential and frictional drag forces that can combine to exceed the formation compressive strength), excessive drawdown causing fines and sand grain movement to the wellbore, or reduction of reservoir pressure. Sand production leads to adverse effects on various components in the wellbore and near wellbore area [Zamberi et al. 2014], such as tubing, casing, flowlines, and pumps, as well as surface equipment [Peden et al. 1984; Lidwin et al. 2013]. In addition, sand production may allow for the creation of downhole cavities [Peden et al. 1985] resulting in loss of structural integrity of the reservoir around the wellbore and ultimately possible collapse of the wellbore. Along with these possible issues, there is an additional economic impact in that sand must be separated out and disposed of at the surface and can be a few liters to several hundred cubic meters [Lidwin et al. 2013]. Decisions around sand production are not purely economic these days because regulatory and environmental restrictions have come to play a significant role in the decisions of how sand production will be handled. In general, what constitutes an acceptable level of sand production depends on operational constraints such as the ability to use erosion resistant materials, fluid separator capacity, sand disposal capability, and artificial lift equipment's capability to remove slurry from the well, but with that said, sand control methods that allow unconsolidated reservoirs to be exploited often reduce production efficiency. Thus, an effective design is always a balance between keeping formation sand in place without unduly restricting current and future productivity [Saucier 1974; Mathis 2003; Palmer et al. 2003; Lastre et al. 2013]. There are two primary methods of sand control these days, namely passive and active, where passive sand control uses perforation orientation and placement to try and mitigate sand production, while active sand control uses a more intrusive approach utilizing downhole filters [Tibbles et al. 2020]. Currently, the most popular and successful method of negating sand production is gravel packing around a downhole filter. In this method, gravel is deposited downhole by pure beta wave deposition in slightly deviated wellbores, i.e., wellbores having a deviation angle in the screen section less than about 50 degrees, or by what is normally referred to as alpha/beta wave deposition in highly deviated wellbores, i.e., wellbores where the screen section maximum deviation is greater than 50 degrees.
Sand, or fines as some may call it, entering currently producing wells is one of the earliest problems faced by the Oil and Gas Industry in hydrocarbon recovery [Rogers, 1954; Carlson et al. 1992; McLeod 1994; JPT Staff 1995; Barrilleaux et al. 1996], and one of the toughest to solve in general [McLeod 1997]. Every year the petroleum industry spends significant capitol in cleaning and disposal costs, repair problems related to sand production, and lost revenues due to lower production rates due to mitigation efforts [Mathis 2003; Palmer et al. 2003]. Thus, sand control is, and should be, an integral part of well planning [Guerrero 2014] in unconsolidated reservoirs [Willson et al 2002; Chang 2006; Jaimes 2012], i.e., reservoirs where the rock has little or no natural inter-grain cementation. Sand production [Veeken et al. 1991; Subbiah et al. 2021] is caused by structural failure of the borehole wall rock due to drilling, degree of consolidation (very low compressive strength), the interaction between the rock and flowing fluids (production creates pressure differential and frictional drag forces that can combine to exceed the formation compressive strength), excessive drawdown causing fines and sand grain movement to the wellbore, or reduction of reservoir pressure. Sand production leads to adverse effects on various components in the wellbore and near wellbore area [Zamberi et al. 2014], such as tubing, casing, flowlines, and pumps, as well as surface equipment [Peden et al. 1984; Lidwin et al. 2013]. In addition, sand production may allow for the creation of downhole cavities [Peden et al. 1985] resulting in loss of structural integrity of the reservoir around the wellbore and ultimately possible collapse of the wellbore. Along with these possible issues, there is an additional economic impact in that sand must be separated out and disposed of at the surface and can be a few liters to several hundred cubic meters [Lidwin et al. 2013]. Decisions around sand production are not purely economic these days because regulatory and environmental restrictions have come to play a significant role in the decisions of how sand production will be handled. In general, what constitutes an acceptable level of sand production depends on operational constraints such as the ability to use erosion resistant materials, fluid separator capacity, sand disposal capability, and artificial lift equipment's capability to remove slurry from the well, but with that said, sand control methods that allow unconsolidated reservoirs to be exploited often reduce production efficiency. Thus, an effective design is always a balance between keeping formation sand in place without unduly restricting current and future productivity [Saucier 1974; Mathis 2003; Palmer et al. 2003; Lastre et al. 2013]. There are two primary methods of sand control these days, namely passive and active, where passive sand control uses perforation orientation and placement to try and mitigate sand production, while active sand control uses a more intrusive approach utilizing downhole filters [Tibbles et al. 2020]. Currently, the most popular and successful method of negating sand production is gravel packing around a downhole filter. In this method, gravel is deposited downhole by pure beta wave deposition in slightly deviated wellbores, i.e., wellbores having a deviation angle in the screen section less than about 50 degrees, or by what is normally referred to as alpha/beta wave deposition in highly deviated wellbores, i.e., wellbores where the screen section maximum deviation is greater than 50 degrees.
A significant recent advancement in sand control technology is the use of diverter subs in conjunction with shunt tube gravel packing, further increasing the application window of this popular technique. This follows several reported cases where excessive amounts of slurry were lost to the formation after exceeding the fracture pressure and, despite the use of shunts, the screen annulus was not completely packed. Diverter subs minimize this risk by allowing fluid to bypass portions of the wash-pipe, which helps to reduce bottom hole pressure and maintain it below the fracture pressure. However, this effect is heavily dependent on the number and placement of diverter subs, so effective modelling becomes critical as improper design may still fracture the formation and result in an incomplete pack. The introduction of diverter subs results in fluid being distributed in multiple directions at various points along the wellbore, making the flow path progressively harder to model as the number of subs increases. Consequently, no models existed that could accurately design or evaluate shunted gravel pack treatments with diverter subs. This paper discusses the development and validation of the industry’s first simulator which incorporates diverter subs with a commercially available gravel pack model to accurately design their optimal number and placement. This was validated with a case history using both shunts and diverter subs, confirming the model can accurately design and evaluate these complex treatments. The paper further extends this work to demonstrate how the model can be used to optimize future designs, expanding the application window of these treatments into tight pore-frac margin wells by reducing the risk of incomplete packing.
The Angelin field lies off the Southeast coast of Trinidad. Development of the field commenced in 2018. The end of the useful life in certain wells created a chance to economically tap into the smaller reservoirs within the Angelin Field. This was achieved by repurposing and refurbishing the wellbores from the depleted wells. This process entails removing existing completion equipment (Decompletion), abandoning the previously exploited zone, and then drilling towards a new reservoir. Sidetracking operations are performed to target the new zone. This is typically achieved by either cutting/retrieval of production casing or sidetracking of the current installed production casing. The decision is a factor of target location, production casing size and cement placement across casing sizes. Once the wells are drilled to TD, a new completion is installed. The completion design is known as Slim Open Hole Gravel Pack completions, so-called ‘slim’ due to the reduced size of the lower completion section, which is required to pass through the smaller ID production casing. Gravel packing has been employed in the Angelin field as the method of choice to manage sand production from unconsolidated and fragile subsurface formations in a high-rate gas environment. A distinctive characteristic of open-hole gravel pack (OHGP) compared to other sand control methods is its specialized screens. These screens contain ancillary shunt and transport tubes welded onto its core structure designed to achieving reliable sand control within the wellbore by providing alternative pathways for the gravel should there be any flow obstructions in the open hole. Although these features increase the reliability of the gravel pack job, they also introduce new potential failure points during installation to an already sensitive component of the well completion setup. Figure. 1Angelin Field offshore the island of Trinidad Other critical components of the Angelin design include a fluid isolation device, gravel pack packer, gauge assembly and safety valve. Figure. 2Angelin Completion DesignFigure. 3Angelin Drilling Design During the recompletion of one of the Angelin wells, the well was unable to be delivered as designed during well execution due to stuck pipe (production liner) above the reservoir interval which eliminated the initial plan of accessing the reservoir with the base case design. The option available for progressing the well was to access a shallower target across the stuck pipe via section milling or whipstock. The paper discusses the deployment considerations for both options and the eventual execution strategy used to successfully circumvent the high risks of deploying a slim-hole completion through a milled window.
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