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Experimental investigation of proppant transport and behavior in horizontal wellbores using low viscosity fluids
Ahmad, Faraj A.
Ahmad, Faraj A.
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2020
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2020-12-04
Abstract
Hydraulic fracturing has become a widely applied technology for stimulating low permeability reservoirs. The reason for stimulating tight formations is to increase recoverable reserves and to accelerate production. This can be accomplished by placing hydraulic fractures in the targeted formations to allow the flow of oil and/or gas from the reservoir to the wellbore. These fractures are created by pumping a fracturing fluid at a high flow rate and then introducing proppant with the fluid to keep the fractures open after the pumping is stopped. One of the most significant concerns in this process is the proppant transport and distribution between multiple perforation clusters. Uneven proppant distribution between multiple clusters/fractures can lead to a reduction in the fracture conductivity, which in turn impacts the viability of the entire hydraulic fracturing treatment. Even though hydraulic fracturing technology has made substantial progress over the last several years, proppant transport and distribution in multiple hydraulic fractures is not fully understood. The objective of this experimental research is to evaluate proppant transport and behavior in horizontal wellbores using freshwater and high loading friction reducer (HLFR)-based fluids. More specifically, the focus is to experimentally investigate the parameters that have a large influence on proppant distribution between perforation clusters. These parameters include, but are not limited to, proppant concentration, injection rate, fluid viscosity, and proppant type and size. This approach utilizes a model of a 30-foot horizontal wellbore with three perforation clusters. Four shots per foot with 90-degree phasing were designed around the pipe for each cluster. Fresh water without additives was used to simulate slickwater fluids. Tests were also run using a commercial HLFR fluid system. The elasticity and the viscosity of the HLFR fluids were measured under a variety of shear conditions across a wide range of HLFR loadings. Experiments were carried out on 20/40 and 40/70 mesh sand and ultra-light weight (ULW) ceramic across a wide range of proppant concentrations. The injection rate/slurry velocity was varied throughout the experimental tests. The results from this work using freshwater fluids showed that 20/40 and 40/70 mesh sand at low flow rates exhibited highly uneven proppant distribution among the perforation clusters. The gravitational forces were more dominant over the momentum forces resulting in more proppant received by the first cluster. However, at higher flow rates, the amount of proppant received at the toe cluster was higher than the amount of proppant received at the other two clusters. This occurred because the total momentum forces near the first and second clusters were relatively higher than the gravity forces. This resulted in some proppant particles not being able to make a complete turn into perforations within the clusters. On the other hand, the results from the experimental runs conducted on 20/40 ULW ceramic showed good uniform proppant distribution across each of the perforation clusters. The 40/70 ULW ceramic showed the most uniform proppant distribution between the perforation clusters. The small difference in the momentum between the proppant and the carrier fluid and also the smaller particles can cause the proppant particles to distribute more uniformly in the fluid resulting in even proppant distribution between the perforation clusters. The results of the rheological properties measurements for HLFR fluids showed that as the shear rate increases for these fluids, the fluid viscosity decreases. Experiments at low flow rates and low loadings of HLFR gave results similar to freshwater fluids for both 20/40 and 40/70 mesh sand. The first cluster received more proppant than the first and the second clusters. The results demonstrate that the 20/40 mesh sand cannot be suspended efficiently in the horizontal wellbore even at relatively higher fluid viscosities (up to 17 cp in these tests). The 40/70 mesh sand showed the most uniform distribution between the perforation clusters at relatively higher fluid viscosity, where the viscous forces were very significant in the fluid flow. The experimental results were used to develop four types of correlations for 20/40 and 40/70 mesh sand and ULW ceramic. These correlations can be used to predict the proppant distribution between the perforation clusters. The first correlation type is based on the proppant concentration, while the second type is based on the flow velocity and proppant concentration. The third correlation type includes the particle diameter as another independent variables along with the flow velocity and proppant concentration. The fourth and final developed correlation includes the proppant density along with the proppant median diameter, flow velocity and proppant concentration as its independent variables. This fourth and final correlation was verified by comparing its predicted values to the laboratory values. The results of correlation analysis on the developed correlation show that the ULW ceramic showed low error values compared to sand at low flow velocities. The low error values indicate high reliability of the developed correlation in predicting the proppant distribution between the perforation clusters.
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