Modelling the Impact of Stacking Patterns and Fractures on the Connectivity of Deltaic Reservoirs

Deltaic reservoirs are important reservoirs for the oil and gas production. Most of the hydrocarbons produced from deltaic reservoirs are obtained from the matrix or primary porosity. Besides primary porosity, secondary porosity, formed after deposition takes place, can have a positive contribution on hydrocarbon production. One of the processes that form secondary porosity is fracturing in addition with the addition of dissolved grains and cements. However, the role of fracturing is surprisingly unknown for one of the leading reservoir types in the world. Stacking of sediment packages is cyclic base level change causes the stacking of sediment packages. It commonly occurs in the deltaic system and gives rise to a high degree of interaction between sand and shale. This interior interaction between sand and shale will affect the connectivity of the reservoir, especially vertical connectivity (it could lead to permeability baffles or barriers). Sand to sand contacts are the favourable spots for connectivity to exist, hence, it is impractical to just rely on the sand to sand contacts to maximize the hydrocarbon production. Fractures might be one of the factors that influence the reservoir connectivity besides the sandstone to sandstone contacts, especially if fractures are open and not filled by cements or minerals. The presence of fractures only gives small additions in pore volume, but the biggest impact is that the effective permeability can be increased significantly, affecting the hydrocarbon production. The permeability of fractures is very dependent on the fracture connectivity. Fracture connectivity is a function of fracture intensity, geometry, and orientation. The combination of these parameters mentioned before play a significant role for the development of self-connected clusters, which are networks of connected fractures. The more self-connected clusters within the field, the more hydrocarbons will be recovered (with the assumption of open fractures). The role of fracture connectivity is really dependent on the sandstone architecture in the deltaic reservoirs. It is significant when the reservoir distribution is scattered and no major connected sandstone bodies are formed. The occurrence of fractures, indeed, will increase the interconnectivity of the sand bodies and the effectiveness in terms of reservoir productivity. However, the role of fractures is less crucial on an evenly distributed sandstone together with the existence of major connected sandstone bodies, since the interconnectivity within the sandstone is already preserved as a factor of sedimentological domain. Fractures may only improve the effectiveness of reservoir productivity when connecting the major bodies to the non-connected minor sandstone bodies.Civil Engineering and GeosciencesGeoscience & EngineeringPetroleum Engineerin