Schlumberger

Case Study: FLAIR Service Enables Reduced Development Costs and Increased Production in Highly Depleted Reservoir

FLAIR service identifies fluid phase from surface logging, where results from traditional downhole logging are ambiguous.

Challenge: Identify hydrocarbon phase in zones where logging results are ambiguous—economics of the highly depleted reservoir preclude downhole fluid sampling in every interval of interest.

Solution: Determine reservoir fluid composition cost-effectively through FLAIR fluid logging and analysis in real time.

Result: Resolved ambiguous neutron-density crossover to identify oil-bearing sand, which was subsequently targeted for production.

Depleted reservoir produces ambiguous neutron-density logs

A major operator in Southeast Asia has been producing from a mature oil and gas field—a large, complex field with multiple hydrocarbon zones—for decades. The production process has induced changes in fluid composition with time. For example, gas comes out of the solution as pressure drops below the saturation pressure, or the gas cap may expand into the oil zone. The result is a frequently ambiguous crossover of conventional neutron and density logs, which are commonly run for fluid identification. A zone that appears to be gas-bearing on the log often flows high-GOR oil, leading to much uncertainty in defining the completion program and estimating reserves.

In the subject well, logs acquired while drilling showed a small crossover in one of the targeted reservoirs (Sand B), raising doubts about the fluid type in that zone. Downhole fluid sampling would provide a definitive answer, but project economics prevent widespread use of the technique.

FLAIR analysis provides cost-effective fluid typing

While drilling the well, FLAIR fluid logging and analysis in real time was used to cost-effectively identify formation fluids after calibration with downhole fluid samples from an offset well. The service continuously analyzes hydrocarbons extracted from drilling mud returns at surface, providing C1–C5 composition analogous to the downhole reservoir fluid. In addition, C6–C8 markers, together with methylcyclohexane (MCC6) and light aromatics such as benzene (C6H6), improve fluid characterization.

Analysis identifies oil-bearing sand

FLAIR analysis confirmed the neutron-density log identification of gas and oil in two targeted reservoirs (Sands A and C, respectively). It also resolved the fluid uncertainty in Sand B, identifying this zone as oil-bearing. A suitable cutoff applied to the computed molecular weights clearly differentiated gas and oil fingerprints. Based on this information, a downhole fluid sample was programmed. Results confirmed the fluid type identified with FLAIR analysis.

The operator was able to optimize the completion program for the production well that targeted Sand B. Having demonstrated its reliability in this pilot case, the FLAIR service was systematically run throughout the field. Downhole fluid sampling for fluid identification programs was considerably reduced, resulting in large cost savings.


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FLAIR Analysis Provides Cost-Effective Fluid Typing

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