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Collaborating Authors
This paper was prepared for presentation at the 1999 SPE Annual Technical Conference and Exhibition held in Houston, Texas, 3–6 October 1999.
- Europe > United Kingdom > North Sea (0.89)
- Europe > Norway > North Sea (0.89)
- Europe > Netherlands > North Sea (0.89)
- (2 more...)
- Well Completion > Sand Control > Screen selection (1.00)
- Well Completion > Sand Control > Sand/solids control (1.00)
Abstract Standalone screens (SAS) in openhole can provide highly reliable sand control completions at a lower cost and with less operational complexity than other openhole sand control completions as well as long term productivity performance comparable to other openhole completions, when applied in the "right environment with the right procedures." Although many in the industry would agree with the preceding statement, there is no consensus on what the right environment is and what the right procedures are. Even when there is agreement on the applicability of SAS for a particular sand size distribution, there are considerable differences in the recommended screen type and screen opening between various laboratories. In this paper we critically review the various laboratory testing procedures used in the industry and the interpretations made to evaluate screen performance and screen selection for SAS applications. We demonstrate that the way some of the laboratory tests are performed are biased towards one type of screen (wire wrap) and some are interpreted without sufficient information such that they almost always favor another type of screen (premium mesh). We show that severe screen plugging with clean formation sand is almost never an issue and that the probability of screen plugging due to other factors can be minimized when proper precautions are taken. We propose that screen candidates for standalone screen applications be initially selected based on sand retention performance, with the final selection confirmed based on flow capacity. In addition, based on ~ 185 laboratory tests performed on various types of wire wrap (6 to 16 gauge) and premium mesh (60 to 600 µm) screens for unconsolidated sands and using a set criterion for sand retention, we conclude that many of the currently used criteria in the industry for selection between gravel packing and SAS are highly conservative, and unduly limit the possible application of standalone screens.
- Europe (0.68)
- North America > United States > Texas (0.46)
- North America > United States > Louisiana (0.28)
- Europe > Norway > Norwegian Sea > Halten Bank Area (0.94)
- Europe > United Kingdom > North Sea (0.89)
- Europe > Norway > North Sea (0.89)
- (2 more...)
Summary Over the past few years, several premium sand-control screens have been introduced into the market. The proliferation of new screens has raised questions about how to choose the proper sand-control screen for a particular formation. To address this concern, a project was initiated at ChevronTexaco Exploration Production Technology Co. (EPTC) to devise a method to evaluate sand-control screens. As a result of this program, a method has been standardized for the evaluation of sand-control screens. The method, known as the screen efficiency (SE) test, shows the relationship between normalized sand-control characteristics (i.e., sand-control factor) of the screens and the normalized length of time it takes a screen to plug under a certain set of conditions (i.e., the performance factor). The results of SE tests to evaluate several sand-control screens for a North Sea and a west Africa field are discussed in the paper. The data in this paper also document that the numerical ratings given by the manufacturers are generally not very useful in understanding the sand-control rating of the particular screen or in comparing screens from different manufacturers. In addition, the effect of particle size distribution and sand concentration on the relative performance of sand-control screens was demonstrated by a comparison of SE plots of sands from the North Sea and west Africa fields. Introduction A new generation of sand-control screen known as a premium screen has gained wide acceptance over the past several years. In general, these screens consist of a perforated base pipe, some type of woven metal material layered onto the base pipe, and a protective shroud around the woven metal material. There have been several papers written concerning evaluation of sand-control screens. However, the need for a standard method of evaluating sand-control screens in the oil industry is evident. The ever-increasing number of premium screens and reams of data generated by the manufacturers are confusing at best. The service companies are, in good faith, generating a great amount of data to support the performance of their particular products. In addition, the service companies are usually advertising the sand-control screens with a numerical value, which is supposed to represent some semblance of the size of the openings in the screen. The numerical value is usually based on the results of the glass bead test or some other sieving technique. These techniques involve measuring the largest glass bead or particle that will pass through the screen; however, they do not provide enough information about the ability of the screen to control sand. Information about the plugging tendency and the amount of solids that will pass through a screen is what a practicing engineer really needs to know to decide which is the most appropriate screen for any sand-prone completion. As part of an ongoing program, a method of evaluating sand-control screens on the basis of the relative plugging tendency and the amount of solids that will pass through them was developed by EPTC. Several screens were evaluated for application in the North Sea and west Africa fields to help in the selection of a screen for the next round of completions. The results of the screen evaluations are discussed in this paper along with a detailed description of the testing methodology. Discussion The method developed for the evaluation of sand-control screens, known as the SE test, is based on measuring the pressure buildup and the amount of solids that pass through a sand-control screen sample as a function of time at a constant flow rate of solids-laden fluid. The solids that pass through the screen sample have a simulated particle size distribution for a particular formation and are at a constant concentration in the fluid at all times. Details of the procedure are given in Appendix A. North Sea Test Program Several sand-control screens were evaluated with the SE test to allow selection of a screen type for the next set of completions. The criteria for the screen selection centered on the two previously mentioned aspects of screen performance—screen plugging and sand retention. The first criterion is obvious; it is desirable to have screens that last as long as possible before plugging. The second criterion is easy to understand but difficult to achieve from the standpoint of filtration (i.e., screens that do not plug and do not pass a significant amount of sand). Selection and Preparation of Test Samples. Two small samples of North Sea formation sand were sent to EPTC to verify the particle size distribution of the sands. A portion of each sand sample was cleaned following a procedure provided by a local service company (see Appendix B). The sand was then analyzed with standard sieve-analysis techniques. The result of this analysis is shown in Fig. 1. A synthetic formation sand was then prepared to simulate the particle size distribution shown in Fig. 1 for all the North Sea tests. Screen Selection. The SE test described in Appendix A was used to test the relative performance of several screen types for possible application in the completion of wells in the North Sea formation. The filter media used in this portion of the test program are described in Table 1. Fig. 2 shows the pressure profiles of all the screens tested. Inspection of Fig. 2 indicates three apparent groupings of screens; Table 2 is a listing of these. Even though the information presented in Fig. 2 and Table 2 appears to group the various screens, additional information is critical in the determination of which screen is best for sand control in the North Sea completions. It is very important to know the relative amount of sand coming through each of the screens (i.e., the gravimetrics). Fig. 3 shows the gravimetrics for each of the screens tested. Evaluation of the pressure profile and the gravimetrics for all the screens provides a much more complete evaluation of the various screens. It appears that the Group 3 screen is eliminated as a choice because of the large amount of solids that come through the screen. The Group 1 screens appear to plug too quickly and, therefore, are probably not the screens to use in the North Sea completion.
- Europe > United Kingdom > North Sea (1.00)
- Europe > Norway > North Sea (1.00)
- Europe > North Sea (1.00)
- (2 more...)
Abstract Screens are used to mechanically restrain formation solid entrance to a wellbore. As effective as this process may be, in many cases it fails to retain solids. This is due to screen plugging either during screen run in a wellbore or during production where larger size particles bridge against a screen and finer size particles plug the screen. In either case, plugged screens are subjected to a cleanup treatment. In this paper, a series of large-scale tests are conducted to evaluate screen cleanup methods such as acid spotting, use of enzyme and acid activated-breaker, backflow, and a combination of these methods under downhole conditions. At first, each screen's retention performance is evaluated. Then, a drill-in-fluid containing solids is pumped into a large-scale flow-cell at a constant pressure drop across the screen to simulate a screen run down in a wellbore. Inlet and outlet samples are collected to evaluate removal efficiency of each screen. Then, each plugged screen is subjected to a cleanup method. The effectiveness of each cleanup technique is evaluated based on the retained permeability of each screen. Degree of plugging and percent area open to flow for each screen is also presented. Introduction All mechanical techniques used in controlling sand production are based on the bridging theory. This principle is based on the large size particles bridging against a mechanical filtration device such as a screen that allows the flow of fluid and restrains solids. In many cases, these techniques are not successful. In screen completion, the failure is due to either screens being run into dirty drill-in-fluids, which will cause screen plugging, or when screen is positioned in a wellbore, larger solids bridge against the screen and finer materials will either pass through the screen and onto the wellbore or plug the screen. If finer particles pass through the screen, the problem of local erosion becomes important. In addition, sand production will be an issue. If these fine particles are held by screen, they will eventually plug the screen. Therefore, size selection of solids present in a mud becomes very important because solids must bridge across pore throat properly to form an effective filtercake. Today, various techniques are used to plug and clean screens. Most of the previous works are done on small-scale disk size screen. The cleanup techniques include acidizing under dynamic conditions, acid spotting, use of enzyme breaker, and oxidizer. This study utilizes a large-scale flow-loop to plug screens and then uses various screen cleanup methods under downhole conditions. Experimental Setup Laboratory Flow-Loop A 6-ft long by 6-in. inside diameter high strength Plexiglas flow-cell model was utilized to evaluate screen plugging and various cleanup efficiencies under downhole conditions. The flow-cell model is capable of operating at 300 psi pressure differential and 180°F. The model allows visualization of screen plugging and cleanups. The active screen length used in this study was about 5 ft. One end of each screen was capped, and a 6 in. base pipe was connected to the other end to discharge fluid entering into the screen during a test. To prevent any turbulence effect, a flow-diverter was placed onto the capped end of the screen where fluid was entering the flow cell. As fluid entered the flow cell, it flowed around the screen, simulating a screen run down a wellbore, and was then flowed out of the flow cell through the 6 in. base pipe. Pressure drop across the screen was measured between the inlet point, before fluid entered the flow cell, and at the point where fluid exited the flow cell through the 6 in. blank pipe. Two valves, one at the inlet and one at the outlet, were installed to collect inlet and outlet samples for size distribution analysis of solids in the formulated drill-in-fluid. These data were used to evaluate screen retention capabilities. A Heat tape was wrapped around the insulated flow cell to maintain a constant temperature during acid spotting and or enzyme treatment. Flow rate, pressure drop, and fluid temperature data were electronically collected Fig. 1 shows schematic of the experimental setup. Laboratory Flow-Loop A 6-ft long by 6-in. inside diameter high strength Plexiglas flow-cell model was utilized to evaluate screen plugging and various cleanup efficiencies under downhole conditions. The flow-cell model is capable of operating at 300 psi pressure differential and 180°F. The model allows visualization of screen plugging and cleanups. The active screen length used in this study was about 5 ft. One end of each screen was capped, and a 6 in. base pipe was connected to the other end to discharge fluid entering into the screen during a test. To prevent any turbulence effect, a flow-diverter was placed onto the capped end of the screen where fluid was entering the flow cell. As fluid entered the flow cell, it flowed around the screen, simulating a screen run down a wellbore, and was then flowed out of the flow cell through the 6 in. base pipe. Pressure drop across the screen was measured between the inlet point, before fluid entered the flow cell, and at the point where fluid exited the flow cell through the 6 in. blank pipe. Two valves, one at the inlet and one at the outlet, were installed to collect inlet and outlet samples for size distribution analysis of solids in the formulated drill-in-fluid. These data were used to evaluate screen retention capabilities. A Heat tape was wrapped around the insulated flow cell to maintain a constant temperature during acid spotting and or enzyme treatment. Flow rate, pressure drop, and fluid temperature data were electronically collected.Fig. 1 shows schematic of the experimental setup.
Abstract Some of the completion failures are due to screen plugging. A number of remedies have been adopted by the industry to cleanup plugged screens. However, these cleanup methods are not investigated under downhole conditions. This study utilized a large-scale radial flow-loop to study prepacked screen cleanup under downhole conditions. First, the original permeability of each screen was measured with 10 ppg NaCl brine solution. A sized carbonate drill-in-fluid was then formulated and pumped for 3 hours and at a constant differential pressure of 60 psi across the screen, simulating a screen run in a wellbore. Inlet and outlet samples were collected for size distribution analysis and removal efficiency calculations of each screen. Each plugged screen was then subjected to a cleanup method such as acidizing, use of enzyme breaker, backflow, or a combination of these methods. Following cleanup, the permeability of each treated screen was measured with 10-ppg NaCl brine solution and compared to the screen's original permeability. The degree of plugging and percent area open to flow was evaluated based on the retained permeability of each screen. Introduction In horizontal wells, drilling mud is usually not displaced with a clean brine solution because of the costs. This requires screens to be run into mud, which contains solids. As a result, screens may plug and hence productivity declines. The overall screen plugging may occur due to the presence of various solids in the mud as well as migration of fines from the formation. Therefore, the degree of screen plugging depends on the solids used in the mud and formation fines. Prepacked screens are known to be more vulnerable to plugging due to the pore throat size of pack media. A number of works has been conducted to investigate screen-plugging mechanisms and to evaluate various cleanup efficiencies. Some of these works have focused on the role of drill solids in plugging and drill-in-fluid optimization to reduce screen plugging. Some works have been focusing on screen design and its proper selection to prevent plugging. Others have been concentrating on cleanup evaluation of screens after they are plugged. Also, screen plugging mechanisms and their remedies have been the subject study of some authors. All of these research efforts are informative, but not comprehensive. As a result, more works are being done to fully understand the mechanism of screen plugging under downhole conditions and to evaluate various cleanup methods. These works consist of new screen designs to reduce plugging potential and increase in removal efficiency, development of new enzyme breakers that are more effective and cost efficient, and improved cleanup methods which are more environmentally safe. The objective of this study was to evaluate the efficiency of various cleanup methods using prepacked screens, which are more susceptible to plugging.
- Well Drilling > Drilling Fluids and Materials (1.00)
- Well Completion > Sand Control > Screen selection (1.00)
- Reservoir Description and Dynamics (1.00)