| Popis: |
In the emerging West Africa deep offshore region, where exploration is booming, the turbiditic series reservoirs are mostly structurally trapped with a stratigraphic component. Faulting is severe inducing high compartmentalisation. Evaluation of connectivity and characterisation of the reservoir heterogeneities before development decisions are the main challenges. These two long DST acquired at a relatively early stage of the appraisal were a game changer for the development project. Both demonstrated large scale reservoir continuity in a complex geological setting, which in turn provided extraconfidence on the feasibility of a large scale development project. The confrontation of this wide scale dynamic information to seismic data and geological concepts allowed significant optimisation of the remaining appraisal sequence. Testing methodology, based on Total experience, advocates the setting of two cycles of draw-down and build-up to generate significant depletion between the two build-up's. This test sequence allows discriminating between geological models matching the derivative and assesses a minimum hydrocarbon connected volume. The first case study concerns a third appraisal well drilled to recognise the turbiditic series of Late Miocene age in the Southern panel of a structure discovered recently. This test allowed us to prove a minimum oil connected volume of at least 120 MMbbls, much larger than the pre-test volume of 55 MMbbls estimated from seismic interpretation, and proved an extension of good reservoir facies beyond the seismic visibility limit. In the second case study concerning an exploration well aiming to recognize the turbiditic sands of the same age, the shallower oil-bearing interval was tested. The fault density around the well being quite high, it was important to know if the faults would act as dynamic barriers. This test proved a minimum connected volume of around 90 MMbbls, and indicated that the encountered reservoir facies was developable as the high fault density around the location of the well did not negatively affect the dynamic performance. In this well, only one out of several faults at 130 meters from the well, within the investigated area of the test, acted as a dynamic barrier. |
