The Impact of Fault-Zone Materials from Hydrocarbon Accumulation: From Outcrop Analogue from Southeastern Nigeria

Olugbenga A. Ehinola¹ and Adeboye S. Adeyemi^2
1Geology, University of Ibadan, Ibadan, Nigeria
²OTG-W Dept., Mobil Producing Nigeria Unlimited, Lagos, Nigeria

The contrasting capacity of faults to act as seal in some cases, and to serve as migration conduit in others, has been the subject of numerous researches, especially in the oil industry. However, a lot of previous work on the impact of these faults to hydrocarbon accumulation and production has mostly addressed fault juxtaposition, rather than the properties of fault zone materials, as the sealing mechanism.

The aim of this study is to analyse the relative impact of fault gouge materials and fault juxtaposition as sealing mechanism, and to develop a method to predict fluid transmissibility and / or containment by fault zone materials, using outcrop dataset obtained from southeastern Nigeria. In addition to field mapping and detailed description of fault zone and juxtaposed materials at the outcrop, integrated modeling of fault surface and elevation data and estimation of the permeability of the studied fault using GXII and Shale Gouge Ratio respectively were adopted. To minimize the limitation of the lack of good 3D seismic, pressure and production data, analogous data from other locations of similar geologic settings are incorporated.

The result shows that four different scenarios were possible in the study area and these include: sand-sand, sand-shale, shale-sand and shale-shale relationships across the faults. The attribute from each of these lithologic pairs was integrated with the properties of the fault zone materials to develop a relative impact-matrix for ranking the different scenarios. It can be deduced that both the nature of materials juxtaposed across a fault and the character of materials in the fault zone play significant, and complementary roles in fluid control across a fault. This suggests that field study approach can be adopted in investigating the impact of fault zone materials.

AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery