The SongLiao basin, in north-eastern China, is one of the largest oil and gas basins in China. The volcanic Reservoir underlying the conventional oil bearing and sedimentary reservoirs of SongLiao basin is proven to be huge gas-bearing reservoirs. One deep gas-bearing volcanic reservoir called HaerJin field in the south of SongLiao basin was found recently. As a result of this new find, a joint study project was initiated to perform an evaluation of all available data from existing and new wells, with the objective of calculating gas in place.
The lithology features of the volcanic reservoir of Haer Jin structure are described and the main problems faced are saturation evaluation. Resistivity based methods for saturation analysis have proven to be unsuccessful for this kind lithology. Based on the study on large numbers of core data and the relationship between CMR T2 distribution and capillary pressure curves, one method which has been employed in the study is the calculation of pseudo capillary pressure curves from CMR T2 distributions, and calculation of saturation from the resulting capillary pressure curves.
In the volcanic gas reservoirs, it is difficult to get the formation fluid saturation and gas-water contact from conventional wireline logging data, because of the complicated volcanic mineral composition and petrophysical properties. For the first time, the FWL (Free Water Level) of volcanic reservoir is successfully estimated based on pressure data analysis, which improves the calculation of fluid saturation based on pseudo capillary pressure curves from CMR.
The accuracy and applicability of this formation evaluation approach was proved by the following new drilling wells. The significance of this study is to open one idea for formation evaluation in unconventional reservoir.
This paper will focus on saturation evaluation of the volcanic reservoir in Ha'erJin of the southern Songliao Basin, PetroChina Jilin Oilfield.