Abstract

This paper presents a successful integration of pressure transient tests, production, and seismic data to detect inter-reservoir communication between Hanifa and Arab-D reservoirs in the southern dome of Abqaiq field in Saudi Arabia.

Even though Hanifa and Arab-D reservoirs are separated by about 300 feet of impermeable Carbonates, the two reservoirs are in pressure-fluid communication through conductive faults/fractures in the heavily faulted/fractured area of Abqaiq field.

Late time pressure anomalies on the log-log plots were observed on several field examples of transient tests in Hanifa reservoir and some were interpreted as external effects of pressure support from the communicating Arab-D reservoir. Simulation modeling was used to further analyze such pressure responses.

Better reservoir management decisions and more focused development strategies can be achieved through the utilization of the quantitative pressure transient analysis of those tests.

Introduction

Abqaiq field in Saudi Arabia was discovered in 1940 and production of its oil-bearing reservoir began in 1946. The field is composed of several carbonate reservoirs. Arab-D, Hanifa, and Hadriya are three of its reservoirs on top of each others.

Hanifa reservoir is a very low permeability reservoir (average ~ 1 md) that is separated from the relatively highly permeable Arab-D reservoir (average ~ 400 md) by a thick (~300 ft), non-porous, impermeable, Jubaila formation. Below Hanifa, lies Hadriya reservoir which is lower permeability than the Arab-D, but higher permeability than Hanifa.

The 3D seismic surveys acquired in the 90's highlighted the existence of faults/fractures in Arab-D and Hadriya reservoirs. Loss circulation while drilling horizontal wells, along with production logs provided tangible evidence of existing conductive faults/fractures. Drilling horizontal wells also indicated the existence of sub-seismic faults which cannot be detected by the 3D seismic resolution.

Even though the seismic data quality deteriorates at the Hanifa reservoir and clear reflectors cannot be seen due to the transitional boundary and the small contrast in acoustic impedance, it was possible to delineate faults/fractures in Hanifa reservoir. This was accomplished by interpreting similar features at the Hadriya and Arab-D reservoirs (sharper boundaries and larger acoustic impedance). When the same feature appears in both reservoirs, then it must also exist in Hanifa for it lies between Arab-D and Hadriya. Conductive faults/fractures that cut through these reservoirs are thought to be responsible for the pressure-fluid communication between these reservoirs. Communication between Arab-D and Hanifa is evident through pressure histories of the two reservoirs following the same pattern (Figure-1).

Well testing is the dynamic data that identify seismic and sub-seismic faults inside Hanifa reservoir where seismic data results are inconclusive. The identification and characterization of these faults/fractures have become increasingly important due to increased horizontal well drilling and future multilateral wells in this field.

The ability to distinguish conductive faults/fractures connecting two reservoirs by pressure transient analysis allows for better understanding of the inter-reservoir communication. Moreover, data integration provides a major advantage as to how to detect these faults by reanalyzing existing pressure transient and 3D seismic data.

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