No available data for evaluating stimulation fluids

An operator in the Gulf of Mexico (GOM) was employing stimulation treatments with HCl and organic acid blends to enhance the injectivity of perforations before conducting hydraulic fracturing. The operator was considering the use of alternative stimulation fluids containing HF to exploit its potential to dissolve siliceous damage in the crushed zone around the perforation tunnels. However, the high HSE risks associated with HF had discouraged the operator from conducting laboratory studies. As a result, no data on HF was available to evaluate its effectiveness for stimulating perforations in the field.

Field-specific sandstone acidizing tests—including HF

To provide the previously unavailable data on HF, researchers at the Schlumberger Productivity Enhancement Research Facility (PERF) laboratory designed and performed a series of first-of-their-kind laboratory experiments for the operator. Representative sandstone outcrop cores were perforated with big hole charges and then stimulated with HCl and HF acid blends at a test temperature of 200 degF. The test conditions were tailored to simulate the high-pressure formation characteristics and complex well completions. An injection sequence of eight fluid stages was pumped through the cores using a customized automated system.

Quantified acid performance with unique insight to stimulation mechanisms

The sandstone acidizing experiments showed that a proposed mud acid blend (9/1.5 HCl:HF) increased the permeability of the perforated sandstone cores by about a factor of two. Surprisingly, comparable performance was obtained with the baseline acid currently used by the operator (10/10 HCl:acetic acid [HOAc]).

The digital analysis of the tested cores included computerized tomography (CT) scans, thin-section analysis, and scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS) to understand the mechanisms underlying the stimulation results. The analysis revealed that permeability enhancement is dominated by HCl dissolution of iron oxide, gun scallop, and casing debris deposited in the perforation tunnels during the perforating event and is achieved irrespective of the use of HF.