Case Study: PowerJet Omega Charges Greatly Reduce Skin Factor in a Vietnam Appraisal Well for Premier Oil Vietnam

Reservoir potential proven based on appraisal well performance

Challenge: Significantly reduce skin compared with the initial exploration well and validate a field development plan.

Solution: Design a perforating job by using PowerJet Omega deep penetrating perforating shaped charges to minimize damage and skin.

Result: Reduced skin factor from 7 in the first well to less than 1.

Reduce skin factor and validate a field development plan

Premier Oil plc wanted to prove reservoir potential and characterize dynamic reservoir properties in a new exploration block offshore Vietnam. The first exploration well drilled in this block was successful, testing more than 2,000-bbl/d light oil, but well productivity was considerably below projections. The productivity index was a disappointing 1.3 bbl/d/psi. Premier determined that the perforating operation in the second well would need to be optimized to improve productivity.

In addition to validating fluid properties and proving commercial rates, a key objective in improving the productivity of the appraisal well was to significantly reduce skin from its level of nearly 7 in the first exploration well.

Schlumberger designed optimized PowerJet Omega perforating operation using SPAN software

Data from the first well were carefully reviewed to understand the low productivity. Transient analysis revealed a high skin factor, varying from 4 to almost 7, and a permeability from 10 to 20 mD.

The high skin factor could be explained in part by the drilling practices. To contain uncertain reservoir pressures and minimize the drilling risks, the mud weight had been kept high, with hydrostatic pressure well above reservoir pressure.

At the same time, low permeability had prevented a rapid buildup of mudcake, and an excessive amount of filtrate invaded the formation, creating a damaged zone. The HRLA high-resolution laterolog array showed an invasion radius of approximately 20 in that contributed to the high skin value. The 4½-in gun loaded with standard charges could not penetrate the 95⁄8-in casing beyond the damaged zone.

When this information was entered into SPAN Schlumberger perforating analysis software, a skin factor very close to the one measured was computed.

Using calibrated openhole log and well test results from the exploration well, SPAN software simulation showed that the perforating operation could be optimized—and Premier’s objectives achieved—by using PowerJet Omega deep penetrating charges.

Skin factor was reduced to less than 1 from almost 7

Transient analysis conducted after the appraisal well had been perforated showed that the skin factor was reduced to less than 1 from almost 7 in the first well.

With the skin reduction delivered by PowerJet Omega deep penetrating charges, Premier Oil was confident that it could achieve commercial production and validate its field development plan.

Download: PowerJet Omega Charges Greatly Reduce Skin Factor in a Vietnam Appraisal Well for Premier Oil Vietnam (0.90 MB PDF)

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