Proppant transport characterization of hydraulic fracturing fluids using a high pressure simulator integrated with a fiber optic/LED vision system

Slurries of selected hydraulic fracturing fluids such as 40 lb/Mgal HPG linear gel and borate-crosslinked 35 lb/Mgal guar gel were evaluated to characterize their proppant transport properties using 6 ppg 20/40 mesh sand. In addition, fluids such as water, 40 lb/Mgal HPG linear gel, and borate-crosslinked 35 lb/Mgal gel were evaluated to determine their relative ability to remove the fluidized layer lying along the top of settling proppant bed and to subsequently erode the more compacted layers below. The experimental study utilized a unique high pressure parallel plate flow cell, simulating a downhole fracture, integrated with a vision system of fiber optic and Light Emitting Diodes (LED). The vision system was used to quantify proppant transport characteristics and to study various aspects of proppant transport including bank buildup. Selected hydraulic fracturing slurries were pumped into a high-pressure flow cell having a 0.375 fracture gap width. The slurries were pumped through 3000 ft of 1.188 in. ID coiled tubing, 500 ft of 2 in. ID heat exchanger, and a 2.75 in, inlet manifold that could be configured to represent a wellbore having various perforation arrangements. Slurries were pumped for a selected time at a fixed shear rate in the range of 60 to 120 sec -1 to observe the rate of bed sedimentation. These initial slurry injections were followed by various fluids and slurries to assess the degree of compaction within the previously deposited bed. Data analysis indicates that slurry sedimentation in polymer solutions follows a non-linear relationship with time at a fixed shear rate and that perforation configuration affects proppant transport, bed height growth, and proppant bed wash off near the wellbore. It is also shown that bed height growth is not directly proportional to shear rate. Results from the current study also show that the fluidized layer along the top of the proppant bed is easily removed by a clean crosslinked gel. However, erosion of the more compact underlying layers was found to depend on a number of factors. Among these factors are the type of slurry which formed the deposit, the type of fluid or slurry being used in an attempt to erode the bed, and the total pumping time devoted to eroding the bed.