THE EFFECT OF SAND SORTING ON GRAVEL PACK CHAIRUL ABDI SUPERVISOR: MR. ARIFF BIN OTHMAN PETROLEUM ENGINEERING DEPARTMENT FACULTY OF PETROLEUM AND RENEWABLE ENERGY ENGINEERING UNIVERSITI TEKNOLOGI MALAYSIA AbstractA laboratory research study has been conducted to investigate the effect of sand sorting on gravel pack towardpermeability. Several experiments have been carried out by using a transparent cylinder shape Perspex materialsand holder with diameter 5cm and 25cm length. By using five samples of sand with different sorting andmedian grain sizes, a model was designed to simulate a production zone. Fresh water and diesel with 3.57 cp ofviscosity were used as injection fluid at various flow rates and outlet pressure had been set at an atmosphericpressure. The experimental result reveals that the permeability of sand greatly reduced when smaller size of thesand present in formation because of smaller pore throat and greater resistance to flow. Permeability reductionbecomes more significant when the sand distribution is poorly sorted and the higher injection fluid flow rateapplied. In this study, it is also found that high viscosity of injection fluid will give higher permeabilityreduction. In addition, injection fluid under the continuous flow conditions is always given the higherpermeability compare to discontinuous flow condition. surface production facilities, then the problem ofIntroduction sand production will cause new problems in the next. Sand problem is one of oldest and critical In addition, the installation of gravelproblem in the production wells faced by most ofthe oil and gas production companies due to packing is one of the ways to overcome sandinstability of formation sand is the inflow of production problem. There is much research wasformation sand with hydrocarbon, and it is one conducted due to this particular problem such asissue that cannot be easily solved. sand control; gravel packing. Expected by installing gravel packing sand problem can be Reservoir can absorb and accommodate a solved. Otherwise, by installing a gravel packinglarge volume of hydrocarbon, and permeable sands these other things are also very important, flow ratepermits oil and gas hydrocarbons to flow to and pressure drop is often overlooked.production wells easily. However, in addition to the As a result, to optimize oil and gasmany things that are so beneficial, porous and production in the oil or gas field, especially in apermeable sand is not good enough in the knots poorly consolidated formation, further studies are(poorly cemented). Therefore, when the fluid has required. This project was undertaken to study thestarted to flow into producing wells, thus releasing effect of sand sorting on gravel pack, which maythe reservoir began to crush the grains of sand into cause the sand production problem.the production wells. When oil and/or gasproduced, then the grains of sand are alsoproduced. Methodology Besides reducing the volume of oil and The apparatus had been used in thisgas during production, resulting from sand project consist of sand holder with several piping,production can also reduce the pressure. And if pump, and manometer tube. Before experimentuncontrolled sand production could reach to the conducted, several preparations regarding to the
2experimental apparatus had been prepared as pack permeability for zone 1 of whichfollows: measurement starts from P0 to P1. K1 and K2 are the measurement from zone 2 and zone 3 1. Design and fabricate a sand holder. respectively. However, the primary concern of this 2. Calibrate flow rate of pump. study is with the permeability measurement for 3. Design and prepare formation sand. zone 2 and 3, which are K1 and K2. The result 4. Prepare injection fluid. presented in this report is collected from 5. Conduct the main experiments. permeability K1 and also K2 respectively. The experiments were conducted with Figure 1 shows the schematic diagram of water as injection fluid with 1.0 cp of viscosity andthe experimental apparatus; Figure 2 reveals the three experiments were used more viscous fluid,sand holder design configuration and for Figure 3 which was diesel as injection fluid with 3.57 cp ofto 5 exposes the photographic view of experimental viscosity. The objective was to determine theflow system, sand holder and also U-tube relationship between the sand pack permeabilitymanometer. with the experiments flow time in certain conditions. In the experiment, the permeability wasResult and Discussion determined by using Darcy’s equation. This equation had been used since it is applicable in Several experiments were conducted to laminar flow with the porous media is 100 percentinvestigate the effect of sand sorting on gravel homogeneous with the following fluid and the fluidpack. The experiment was done on unconsolidated is not reacted with the particles (glass beads).sand under continuous and discontinues flowcondition. The outcomes of concern in thisinvestigation are: Formation Sand Grain Size Distribution i. The effect of particle size The grain size of the unconsolidated sand distribution on unconsolidated used in this study was measured using dried sieving sand technique. Five types of sample with different grain ii. The effect of flow rate change size distribution were labelled as sand A, B, C, D due to time iii. The effect of injection fluid and E were used to demonstrate that different size viscosity distribution that may cause different permeability. iv. The effect of sand sorting In Figure 6. shows that the formation sand v. The effect of permeability distribution that had been used in this experiment. responds to flow condition. The graph on figure 7. shows the pattern of particle size distribution for these five samples. From this graph, the median particle size, which is Flow rate changes under continuous flow D50 for each sample was measured and uniformitycondition mean that the flow rate will be started at coefficient, C; which is D40/D90 can be calculated20 cc/s for 60 minutes before being increased to 30 for each sample. From this graph shows all fivecc/s for 60 minutes and finally increased to 50 cc/s samples have significantly differ in its sorting.also for 60 minutes. Under the discontinuous flow Sorting sample was a measure of deviationconditions, the flow rate will be started with 20 cc/s both from the median diameter to given a normalfor 60 minutes before switching off the pump for distribution of grain sizes, both larger and smaller20 minutes and then increased the flow rate to 30 are present in the total population of sand pack. Thecc/s also for 60 minutes. And finally, flow rate 50 sand size distribution graph in Figure 4.2 indicatescc/s will be applied after the pump switch off for 20 that sorting, D40/D90 for all samples varies fromminutes. 1.3 to 10.6. The median sand size for Sand A, D50 is 130 μm and D40/D90 is 1.6. San A, B, and C Figure 2. shows that the schematic consider as uniform regarding to the Uniformitydiagram of the sand holder. This sand holder is coefficient; C is less than three (C < 3). But, sanddivided into three phase zone for the pressure and size for Sand D is consider as non-uniform andpermeability measurement. K0 represents the sand sand E is consider as very non-uniform / very non-
3sorting this is due to the value of D40/D90 both pressure drop toward permeability, which wassample was very large. Which was uniformity converted to permeability data with varying flowcoefficient for Sand D are 7.6 and 10.6 sand E. rates. In each test, the injection fluid was injected under continuous and discontinuously circulated Permeability is the ease with which fluids for about 60 minutes at each constant flow rate.flow through a rock or sediment. A rock is The permeability was measured periodically, andpermeable if fluids pass through it, and the circulation was continued until the flow rate isimpermeable if fluid flow through the rock is stable.negligible. Normally, permeability depends on;Grain size (Coarser-grained sediments are more In this research study, three different flow rates were set for these experimental studies, whichpermeable than fine-grained sediments because the are 20 cc/s, 30 cc/s and 50 cc/s. Fresh water withpores between the grains are larger), sorting, grain 1.0 cp was used as injection fluid for all fiveshape, and packing (controls pore size). samples. A comparison was made for the results of the permeability against flow time with three different flow rates. There were some fluctuationResponse of the Sand Pack to the Effect of Flow profiles in the graph. This is due to theRate rearrangement of the particles in the sand pack. Flow rate plays an important aspect to Permeability is the ease with which fluids determine the movement of sands particles process.flow through a rock or sediment. A rock is Basically, when the flow rate is become higher, thepermeable if fluids pass through it, and potential of the sand particles to move is higher asimpermeable if fluid flow through the rock is well. These movements occur when the fluids flownegligible. Normally, permeability depends on; rate is unsteady until it reaches a level where theGrain size (Coarser-grained sediments are more progress of the particles stopped after it achieves apermeable than fine-grained sediments because the steady state of the flow rate.pores between the grains are larger), sorting, grainshape, and packing (controls pore size). Effect of Flow Rate on Sand A Permeability According to Darcy’s law, the fluid flow is Figure 8. shows the effect of flow rate onproportionally to the pressure differential between Sand A permeability as measured at K1 and K2.inlet pressure and outlet pressure at constant The results show that with increasing flow rate ofpermeability of the formation. This is only true for the injection fluid it will reduce the permeability ofthe solid-cemented particles (normal sand) such as the sand pack until it became constant after 10core samples but not in a loose pack or minutes of flow time. The reduction wasunconsolidated sands such as gravel packing significantly evident by the different between thecompletion. permeability at flow rate 20 cc/s and 30 cc/s and 50 cc/s for both zones. Generally, the overall behaviour of thesand particulates migration process is critical; this As the permeability for the sample A isis due to the magnitude of the flow rate, since it determined, an analytical study has been conductedaffects the gravel permeability and may cause to discover the relationship between the particleserious plugging problem during high flow rate of grain sizes and permeability over time. From figurefluid. If the flow is too low, no migration of sand 4.3, the lowest injection flow rate gives the highestwill occur, as the fluid flow is not strong enough to permeability. The permeability is estimated aboutcarry particulates, then the permeability is obeying 1200mD for flow rate 20 cc/s, 970 mD for 30 cc/s,the Darcy’s law. Moreover, at high flow rate, a and 820 mD for injection 50 cc/s. Mostly, after 10large amount of particulates is moving quickly, and minutes. The curve shows constant. These arepossibly causing the sand pack to self filtrate after where the flow is reach stabilized and stabilizedsometimes. The self filtration is due to the particles permeability is reached. A huge reduction for flowbuild up within the pores and pores throats, thus, rate 30 cc/s and 50 cc/s curve is due to thecausing the pores to block and the porosity of this instability of the flow. Ironically, for this sampleselement is reducing. The possibility for particles to the tame taken for flow rate to reach its stability ismigrate depends on the compaction forces caused relatively short. This had happened because of theby the flowing liquid. Therefore, the permeability particles in the sample reaching its packingin this layer will decrease, causing a large increase rearrangement in short time and smaller grainin the pressure drop. particle migrate faster to the pore space between bigger grain size particles. A study on the effect of sand sorting ongravel pack was conducted by measuring its
4Effect of Flow Rate on Sand B Permeability no effect on the graph line, it will be at the constant rate. Because at that moment all the particles in the Figure 9. below shows the result for sand pack had reached a dynamic rearrangements.sample B. from the curve below mention that thepermeability at flow rate 20 cc/s is about 1160 mD,followed by 970 mD for injection 30 cc/s and endup with 960 mD for 50 cc/s. From this result it Effect of Flow Rate on Sand E Permeabilityproves that the permeability of each sample, mainlydecrease through the time of different flow rates. Figure 12. The effect of injection flowingGenerally, drop of the value of permeability is fluid rate toward permeability on the sample E. Thehappened in the beginning of the experiment of curve below shows that the permeability is variedeach starting injection applied until the minutes of and very unstable in sometime at the starting point,5th. From the 5th minutes until 10th to 15th this is regarding to rearrangement of particle grainminute, the permeability seems to vary / unstable size due to hydrodynamic force.for a short period, and it seem stable afterwards.This phenomenon is not always occurred at the The Effect of Injection Fluid Viscosityhighest flow rate used where the permeability isdecreasing for a long period but the reducingpermeability is higher when the higher flow rate In Figure 13 through 15 it shows that thewas applied. effect of injection fluid viscosity. There were three samples used in this experiment, which is “Sample C” where represent of uniformity sample. SampleEffect of Flow Rate on Sand C Permeability D represented the non-uniformity and sample E is represented of very non-uniformity. Figure 10. is shown the relationship of thepermeability ratio aver time for sample C. As In all cases, declining of permeability ratebigger particle grain size is being tested, a higher is more significant with 1.0 cp viscosity of water aspermeability is obtained. For this sample, the injection fluid. When diesel is injected into theporosity is 29 percent. It can be seen that the sand pack with 3.57 cp of viscosity it shows that,highest permeability is shown about 1920 mD for the permeability reduction significantly achievedinjection rate 20 cc/s, 1460 mD for 30 cc/s and higher. This is due to the higher lifting power for1452 mD 50 cc/s fluid injection rate. This had more viscous injection fluid, thereby more grainshappened because of particle are stable in slow and particles are invaded and plugged the poreflow rate. The rearrangement of packing are spaces. The increase in viscosity also affects thedifficult to occur and the small particles are not mobility ratio.migrating to the pore space of bigger particle grainsize. In contrast, the force induced in high flow The increasing in permeability of the sandfluid injection are enough to migrate a small pack is due to the increasing in injection fluidparticle and rearranged the packing of particles viscosity. With high viscosity was injected in thehence reduced the existing porosity. sand pack, the grater the permeability reduction was achieved. These phenomena occurred due toEffect of Flow Rate on Sand D Permeability the increase of flowing fluid viscosity will increase the pressure differential too. The increase of flowing fluid viscosity will increase the drag forces Figure 11. shows the experimental result as well. The increase of drag force will cause morefor sample D with 600 µm of Median Grain Size severe plugging on pores spaces and reduces theDistribution. The result shows that the effect of flow path respectively. Because of higher dragflow rate on the Sand D permeability as measured forces have the higher capability to carry particlesat K1 and K2 respectively by using the sand holder. and will increase the pore plugging and minimizeSame as the previous trend, any increasing in the the pore space simultaneously.flow rate will result in the decreasing of thepermeability. The differential value of permeabilityis as follows 820 mD for 20 cc/s, 670 mD for 30 The Effect of Sand Sortingcc/s and 528 mD for injection fluid 50 cc/s. Thecollected data show that a relatively higher The experiment has been conducted toreduction of permeability curve trend than the other identify the effect of sand sorting on gravel packflow rate, which may be due to the rearrangement toward permeability. This experiment only usedof the particle in the sand pack. water at 1.0 cp as injection fluid and at three different flow rates as well as under both Hence, if we continue injecting fluid with conditions; continuous and discontinuously flowthe same flow rate after 60 minutes, there will be condition. The experiments were conducted with
5flow rate at 20 cc/s, and then followed by 30 cc/s yet. Therefore, the increasing hydrodynamic forceand finally end up with 50 cc/s. All five samples will increase permeability reduction respectively.(Sand A, B, C, D and E) had done the sameprocedure. In Figure 16. it shows that, by Field Application of Experimental Resultsincreasing the median grain size it will increase thepermeability value. Base on the experimental result, it shows that good sorting will perform the good In addition, on Non-Uniformity sample permeability. Meaning, in field application, gravelwith 7.6 of Uniformity Coefficient; C and on Very pack needed good sorting. We cannot control theNon-Uniformity sample with 10.6 Coefficient; C in sorting on the formation. But, for gravel packingsample E, presented the very high permeability placement, we can control the sorting. However, ifreduction. This is happened because of non-sorting formation particles (has smaller size particles)particle grain size. The small grain size particles manage to invaded (not penetrate), there is no wayare migrating to the pore space of bigger particle to control them (permeability impairment). Ifgrain size. Thereafter, the force induced in high smaller particles were invaded, the fine grainflow fluid injection are enough to migrate the small particle will plugged the pore throat and it willparticle and rearranged the packing of particles reduce the existing porosity as well. The bottomhence reduced the existing porosity. line here is that we need to control the movement of formation particles at the sand face. At the beginning of the flow time Figure16. shows that all the graph line has fluctuated,these occur at 0 to 30 minutes of flow time. Atthese moments, assumed that all the particles in thesand pack are rearranging each other because of the Conclusionsvelocity of the flow rate. Nevertheless, after 30minutes of flow time due to injection, the Figure The following conclusions can be made based on16. shows that all line at a relatively constant rate. the experiments conducted:So, it is predicted that the particle had reached thedynamic rearrangements. From this plateau region, 1. Higher injection fluid flow rate gaveit shows that the uniform sand distribution which is higher permeability reduction.Sand A, B and C have the highest value ofpermeability compare with non-uniformity and 2. Large median grain size particles withvery non-uniform sand distribution, which is sand the uniformity coefficients; C, lessD and E that had slightly lower value of than three gave better permeabilitypermeability. compared to smaller grain size particles with C value less than three.The Effect of Permeability responds to Flow 3. The sand pack permeability reductionCondition. is more severe when more viscous injection fluid was used. From Figure 16. Generally, permeabilityunder continuous flow conditions is always slightly 4. Good sorting with the uniformitybetter than permeability under the discontinuous coefficients less than three performedflow conditions. These phenomena occurred due to better permeability compare to poorthe packing already reach their stability while sorting with the uniformityflowing fluid flow at 20 cc/s. The particles only coefficients greater than 5.face a small increase of hydrodynamics forcecompare to unstable gravel packing, which had to 5. Gravel packing under the continuousface a higher increment of hydrodynamic force at flow conditions is always rewardedthe beginning of particles movement and the better permeability compared torearrangement before it reached their packing permeability under a discontinuousstability. Therefore, it minimized the pore space flow conditions.sizes and ability of the fluid to flow through thegravel pack besides reduces the permeabilityrespectively. Whereas, for discontinuous flow Referencescondition, the increasing of flow rate will increasehydrodynamics force as well. Higherhydrodynamic force will cause a faster movement 1. BJ Services (1996). BJ Servicesof particles and more sever of plugged at the pore Handbook; Completion Technology forthroat for an unstable/no-cemented gravel pack Unconsolidated Formations. Rev. 3. USA:which the packing had not been reach their stability BJ Services Handbook
62. Yongquan, H., Jinzhou, Z., Zhinjun, W., Zhaofeng, L. “Sand Control Mechanism Analysis of Metallic Wool Screen”. The Petroleum Society Paper 97-1303. Krumbein, W.C., (1942). “Permeability as a Function of the size Parameters of Unconsolidated Sand”. Member A.I.M.E. and G.D. Monk.4. Bellarby, J. (2009). Well Completion Design. 1st ed. Jordan Hill: Elsevier. 183- 184.5. Saucier, R.J., “Considerations in Gravel Pack Design”, SPE Paper 4030, Journal of Petroleum Technology (February 1974), 205-212.6. Xiang, W. and Wang, P. “Application of Bridging theory on Saucier gravel to examine the sand control effect, “China National Offshore Oil Corporation, SPE 80450, April. 2003.7. Leone, J. A. (1990) “Gravel-Sizing Criteria for sand control and Productivity Optimization” SPE 20029.8. Schwartz, D.H. (1968). “Successful Sand Control Design for High Rate Oil and Water Wells”, J. Petr. Tech. 1193-1198.9. Coberly,C.J. and Wagner,E.M (1038). “Some Considerations in Selection and Installation of Gravel Pack in Oil Wells”. Pet. Tech.10. D. L., Tiffin (1998). “New Criteria for Gravel and Screen Selection for Sand Control” SPE 39437.11. Hill, K.E (1941). “Factors affecting the use of Gravel in Oil Well” Oil Weekly. 13-20.12. Gurley, D.G., Copeland, C.T. and Hendrick, J.O.Jr. (1977). “Design, Plan, and Execution of Gravel Pack Operations for Maximum Productivity”. SPE 5709.13. “Recommended Practices for Testing Sand Used in Gravel Packing Operations”, American Petroleum Institute, API Recommended Practice 58 (RP58), March 1986.14. Krumbien W.C. and Sloss, L.L., Stratigraphy and Sedimentation, Second Edition, W.H. Freeman and Company, 1963.