Carlo Sanders¹, Titus A Murray¹, Elizabeth Thompson¹

(1) Midland Valley Exploration Ltd, Glasgow, Scotland

ABSTRACT: Characterisation of fractured basement reservoirs Cuu Long Basin Vietnam using 3D structural and discrete fracture network modelling

The unconventional fractured Cainozoic granite basement reservoirs of the Cuu Long Basin (offshore Southern Vietnam) have proven to be very successful structural oil plays. They demanded adaptation and development of a new reservoir characterisation technique. Structural modelling has proven to be a key component in this process. The reservoir characterisation workflow consists of:

1) Field analogue outcrop studies 2) Construction of a valid structural model 3) 3D kinematic restorations 4) Dilatational and finite strain analysis 5) Building discrete fracture networks models

Field studies of onshore outcropping granites in SW Vietnam lead to the development of a conceptual model of deformation styles and associated fracturing. Tectonic fractures have high fracture density and 3D connectivity compared to cooling fractures. Defining the deformation is therefore of crucial importance to identify the highly fractured sweet spots. Significant bulk deformation occurs in the moving (hangingwall) fault blocks during the mostly extensional basin formation. This deformation is simulated through time using kinematic restorations integrated with 4D finite strain analysis.

The finite strain values along with surface geometry attributes are then used to build 3D discrete fracture networks. The complex variation in the reservoirs fracture density and orientation pattern can be generated using approximations of geological and fracture mechanical processes. The fracture network can be compared to pump tests and iteratively improved. The simulated 3D fracture network is finally used to calculate reserves.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado