Reduced Oil on Cuttings
As drilled cuttings return to the surface and pass through a shale shaker, vibrating screens help separate solids larger than the mesh size and direct them for disposal. Bulk liquid phase containing fines passes through the screens and is eventually returned into active circulation. However, a certain amount of drilling fluid is retained on the cuttings in the form of a thin film and is therefore wasted. In the case of drilling with oil-based fluids, this is referred to as oil on cuttings (OOC). In addition to the direct cost of oil losses, residual oil on cuttings presents an environmental challenge associated with cuttings disposal, especially in sensitive areas, such as in off-shore operations. Recent field tests have demonstrated that OOC can be reduced by up to 38% in the presence of 0.5 wt% nForcer™ compared to control wells that were drilled with conventional fluids.
Oil on cuttings retention is typically measured using retort analysis. The amount of oil on cuttings, which can be expressed either as grams of oil per kilogram of dry cuttings or as cubic meter of oil per cubic meter of dry cuttings, depends on a number of factors, including the type of a drilling bit used, drilling fluid composition, formation lithology, solids processing equipment efficiency, and drilling parameters.
Two sets of two-well pads were drilled in the area north of Hinton, Alberta, Canada. Each pad contained a well drilled with a conventional Distillate 822 85:15 oil-based system (control), which was then compared to a well drilled with the same control system but with nForcer™ added (test). All four wells were horizontal and had a TD of 4,500 mMD. The upper intermediate section between the surface casing shoe (650 mMD) and the kick-off point (2,500 mMD) was drilled with a 222 mm bit and a mud density of 1,050 kg/m3. The lower intermediate section and the production section were drilled with a 156 mm bit and a mud density of 1,150-1,375 kg/m3. Test 1 focused on performance of nForcer™ only in the upper intermediate section, while test 2 contained nForcer™ throughout the entire interval between the surface casing and TD. Two Brandt King Cobra shale shakers equipped with 215 mesh screens were used in all cases. The results of oil on cuttings tests are shown in Figure 1 below.
Figure 1 An impact of the 1st generation nForcer™ nanoparticle additive on the oil on cuttings (OOC) as a function of measured depth in test well 1 (left) and test well 2 (right). Data labels represent the average OOC values throughout the interval tested.
The results suggest that both control 1 and control 2 consistently exhibited similar average values of OOC, 0.81 and 0.77 m3/m3, respectively. Compared to the control wells, the average OOC values in the presence of 0.5 wt% nForcer™ were reduced to 0.50 m3/m3 in test 1 and 0.54 m3/m3 in test 2. This corresponds to 38% and 30% total reduction in the average oil on cuttings retention.
While the exact causes of this behaviour remain unclear at this stage, the results provide a preliminary confirmation that NPs are effective at reducing the amount of oil adsorbed onto the surface of drilled solids. Further tests will be concluded to increase the sample size, improve reproducibility of the data, and determine the mechanism of the effect.
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