Geologic influence on variations in oil and gas production from the Cardium Formation, Ferrier Oilfield, west-central Alberta, Canada

Transcription

1 Geologic influence on variations in oil and gas production from the Cardium Formation, Ferrier Oilfield, west-central Alberta, Canada Marco Venieri and Per Kent Pedersen Department of Geoscience, University of Calgary Summary The Cardium Formation has been a prolific oil producer since the first oil discovery in the 1950s. Recently, the play has been revitalized with the development of horizontal drilling and multi-stage fracturing technology targeting the lower reservoir quality halo play facies. The main aim of this research is to understand the controls on abrupt lateral changes in oil and gas production in the Cardium Formation in the Ferrier Oilfield (base map in fig. 1). In the Ferrier area, the Cardium Formation forms a NE prograding clastic sequence comprised of offshore to shoreface deposits sealed by marine shales. The main reservoir is comprised of sandstones and conglomerates interpreted to have deposited in a shoreface depositional environment. In the western portion of the oilfield the main reservoir body is composed by NW-SE oriented, discrete (2 to 3) clastic packages. An older, gas-charged sandy body is also present 30-40m deeper than the main reservoir in the western area. The older sand sequences shale out to the

2 east, and only the youngest one comprises the reservoir within the eastern Ferrier Cardium Field. Two anomalous production areas in the Cardium were analyzed and interpreted (fig.2). The issue in case 1 is the presence of gas below oil. This is odd as the Cardium in the Ferrier is interpreted to be a laterally continuous clastic body with preserved fluid-dynamic connectivity. In case 1, gas is interpreted to have come from the gas-charged, oldest sand sequence and have reached the youngest sand body comprising the main reservoir migrating through a fault connecting the two reservoir bodies. Once the gas reached the main reservoir, it migrated structurally up-dip towards the NE. The abrupt shift in GOR marks the boundary between the main oil reservoir in the east and the area in the west where gas migrated structurally up-dip. In case 2, a gas-producing area occurs in between two oil producing areas. This is odd as the three sub-compartments have similar depth and core oil saturation values. In case 2, clay cementation is interpreted to be one of the causes for the non-mobility of oil, with a potential role of strike-slip faults causing reservoir compartmentalization. Both in case 1 and in case 2, the solution to the production issue was revealed by Cardium cores. In case 1, one core in particular supports our hypothesis of a fault connecting the deeper to the shallower sand body and acting as a preferential migration pathway for hydrocarbons. This core occurs into a part of the structural map showing presence of potential thrusts and strike-slip faults, and shows that the Cardium is heavily fractured. This indicates potential presence of structural features in the area, supporting our fault interpretation. In case 2, SEM studies on Cardium cores, as well as routine core analyses suggest a difference in cementation between the oil-and the gas-producing area of the Ferrier. The Cardium in the gas-producing area shows abundant illite in the pores, which likely prevents oil from being produced due to the reduced pore throat size within these reservoir sandstones, as core fluid saturation analyses show oil being present in similar proportions as within the oil producing areas. In case 2, cores show mineralized structures in areas of interpreted faults, supporting our interpretation of faults as one of the factors causing reservoir compartmentalization.

3 The Ferrier example offers a unique case of fluid discrimination in tight sandstone reservoirs due both to depositional and post-depositional factors, and could be used as analogue for similar situations in the WCSB and elsewhere.

4 C. I.: 10m Cardium E5 elevation map Fig. 2: Structural map of the top of Cardium E5 marker (2a). Same map with interpreted fault traces and location of the core shown in fig.3. (2b).

5 Fig.3: Core showing fractures in the Cardium Formation. The core lies proximal to an interpreted faulted zone. 10 km 6% Net reservoir map Fig.4: Net reservoir map showing fluid boundaries (red = gas and green = oil) within the Cardium reservoir. A core on a fluid boundary shows a mineralized structure, which is a potential fault indicator.