Location: Kirthar EL. District Dadu, Sindh Province, Pakistan (south central)
Problem: Moderate permeability but tectonically stressed PAB formation with a high degree of Anisotropy becomes difficult to complete. High percentage failure rate in placing proppant.
Pertinent Details: With a higher than global price of gas, the target Upper and Lower PAB zones become desired targets. The Lower PAB has a historic supported poor record of completion failures. Placing any proppant previously had been difficult. The client was focused on placing at least 100,000 lbs. of conductive proppant in the Lower and more in the prolific Upper PAB, but in 2009, very few diagnostic steps revealed why proppant placement was seldom achieved.
Solution: Pre-Frac Diagnostic Fracture Injection test (DFIT) quantified the reservoirs in terms of permeability, reservoir pressure and the stress environment. Little pressure dependent leak-off was observed along with some height regression. Mini-frac analysis revealed the true issue in proppant placement as the near wellbore environment was complex due to extremely low perforating efficiency and high degrees of Tortuosity. However, skillfully using 'Sand-Notching' techniques to access the formation instead of tubing conveyed perforating, the perforation issue was resolved. Then the use of low-volume 100 mesh sand and ramping to 1.5 ppa cleared the tortuosity issues.
Results: At project end, the goal of placing 100,000+ lb. of conductive proppant was achieved and exceeded. The wells were completed with high Initial Potential (IP) values and less rapid declines due to extended proppant conductivity being placed in the formation.
Location: Neuquén Basin, Argentina
Problem: Low permeability discontinuous (mainly lenticular in its depositional environment) from well to well and previously unresponsive to stimulation techniques.
Pertinent Details: Very thick gross footage with 5 to 11 separate lenses scattered over 3000' vertically. The better petrophysical properties were not well known at the time. Classic analysis of logging data revealed that the better wells had poor petrophysical responses or so it seemed. Frac treatments were not working well during the treatments as proppant placement was an issue plus the post-frac analysis indicated conductivity restrictions or limits. The Operator was not clear if gel break was the issue or poor load recovery impeding production.
Solution: The key to candidate or lens selection became the use of calibrating the petrophysics with results from Diagnostic Fracture Injection Testing (DFIT), then high-grade the lenses to eliminate the poor candidates. We performed DFITs on several lenses, then created a chi model to be able to forecast which lenses were the better candidates. The results of the Chi model indicated that the 'standard' petrophysical analysis process was indeed misleading in terms of selecting pay. Frac entry issues were quickly eliminated by first using a higher quality perforating charge and then in some cases, using over-pressured perforating as most of the entry issues were in zones that had minor wash-outs and thicker cement sheaths. The frac treatments were chemically tailored to reflect the load recovery issues as well as chemical additives which had become a marketing issue from one service provider.
Results: The process took several months and after 24+ DFIT and frac treatments we were able to establish a candidate and selection matrix with frac treatment guidelines establishing a decision tree for go/no-go decisions.
Location: Llanos region of Eastern Columbia
Problem: The Barco and Mirador Zones are in a strike-slip and possibly reverse strike-slip environment. Both had a history of allowing a limited volume of fracturing. In other words, attempting to place larger more adequate volumes of fluid and proppant resulted in a screen out. As a fix, the Operator chose to use smaller but slightly inadequate volumes. In many cases, pre-frac production was used to reduce the reservoir pressure but due to a low perm (~ 0.45 MDs) the rates were very low and this process was not adequate for the client.
Pertinent Details: This portion of the Andes The country is located where three lithospheric plates - Nazca, Caribbean, and South American - converge, and their movement produces different types of geologic faults. Almost all of the country's many earthquakes in recent centuries have occurred in the mountainous and coastal regions. The formations were laid down and then uplifted when the South American plate overrode the Andean plate. Then what was the horizontal layer became vertical with more intrusion from the Andes thus the formerly low tension basins were converted to highly stressed zones due to tectonics. This resulted in the vertical wells that were drilled into formerly flat zones now tilted vertically, much like a horizontal unconventional well.
Solution: After using FRACPRO® fracture stimulation software to net pressure match the older completions, the stress environment was identified and a hybrid frac design was employed. Net Pressure analysis offered the cause-and-effect relationship between viscosity and net pressure much like a linear-elastic effect, which reflected that the more viscosity applied the higher the net pressure. However, critical frac width was an issue so viscosity had to be applied in a very cautious way.
Results: Two wells with a total of five zones were completed after adoption of the proposal by the client, record volumes of oil produced as higher levels of proppant were able to be introduced and placed into the Barco and Mirador formations.
Location: Eastern Texas Panhandle - Stiles Ranch, Wheeler County, TX
Problem: Stage spacing with economic solution for frac design.
Pertinent Details: Frac treatments were thought to be fairly optimized but due to rapid production declines, needed to understand fracture spacing and the amount of reservoir drained by each fracture. Economics were key as investor competition was brisk and offset success by competitors was getting much of the airplay in business journals.
Solution: Performed a full characterization study to analyze each lateral to determine the cause-and -effect relationships between reservoir quality based on gas chromatograph and fracture geometry. Net pressure matching using FRACPRO fracture stimulation software yielded significant findings in the stress regime.
Results: One development from production history matching was an apparent restraining of conductivity due to proppant selection. The old designs featured resin coated 40/70 sand with a small volume of 100 mesh at the start. However, there was little evidence of natural fractures which is a bit out of the ordinary for most Granite Wash fields. The gas chromatograph was helpful but not as useful as the gamma ray for selecting the best pay.
The frac spacing plan incorporated increased conductivity using a lite-weight ceramic proppant and removed 100 mesh from the schedule. The first seven wells using the plan averaged 22 MMcfe/day of gas with condensate which was a significant improvement.
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