ABSTRACT

In spring 2017, Hurricane Energy concluded their latest appraisal campaign by drilling three exploration/appraisal wells and one development well in the Greater Lancaster area, West of Shetlands, UKCS. The area is located on the Rona Ridge which is a prominent NE-SW trending basement high. The main target is a fractured tonalite/granitic basement that has undergone a complex tectonic history. Fault Zones, 30–70m wide, are associated with seismic scale faults with preferentially enhanced porosity and permeability; these are targeted by horizontal production wells. The background Fractured Basement is also heavily fractured, and demonstrably contributes to hydrocarbon productivity.

The initial fault recognition based on seismic has been gradually refined and corroborated by drilling results (Slightam 2014). Consequent to extensive evaluation programs, the number of Fault Zones across the field has dramatically increased and a comprehensive picture of the complex network emerged. The ability to confidently link seismic features to reservoir properties is fundamental for field modelling and simulation, particularly when distributing properties away from well control.

Fractured basement reservoirs require a specific approach when acquiring and interpreting formation data and when interpreting the dynamic behavior of the often-intricate flow pathways associated with a hydrodynamic fracture network. An open mindset and expert integration of well data, from different disciplines and different scales of measurement, has been applied and proved essential for formation evaluation in the fractured basement reservoir of the Lancaster Field. Hurricane incorporates drilling parameters, mudlogging data, high resolution gas chromatography, LWD and wireline logs, DST and PLT data to analyze and model the reservoir. It is the combination of these disparate datasets which is key to Hurricane's analysis, as a focus on only one set of data can lead to erroneous conclusions. Advanced logs were combined in novel workflows to characterize the rock texture, litho-facies fracture distribution and effective fracture porosity. DST analysis provides essential information to complete the puzzle, relating the static interpretations to the dynamic behavior of the reservoir.

During the recent drilling campaign, a set of quality petrophysical and geological data were obtained which compare well to the data collected from previous drilling. The consistency in the interpreted data demonstrate a material homogeneity in the reservoir volume associated with the current boreholes. A thorough wireline program on well 205/21a-7, incorporating extensive PLT runs, has been used to infer an OWC that appears comparable to that identified in Lancaster exploration well, 205/21a-4.

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