Core-Log Porosity Permeability Transform (Minas Case Study)



Minas oilfield, one of the largest oilfields in Southeast Asia, is operated by PT. Caltex Pacific Indonesia, a Production Sharing Contractor with Pertamina. The field is located approximately 35 kilometers Northeast of Pekanbaru. The size of the field is approximately 12 by 25 square kilometers (Figure 1). The oil production mostly comes from the Sihapas group, at an average depth of about 2500 feet.
Permeability is one of the most critical factors in producing hydrocarbons and for simulation study. Permeability of a rock depends upon the effective porosity; therefore, permeability is affected by the texture of sedimentary rock i.e.: grain size, grain shape, grain size distribution (sorting), grain packing and the degree of consolidation and cementation. Permeability is also affected by the presence of clay type, especially where fresh water is present. Some clays, particularly smectites (bentonites) and montmorillonites, swell in fresh water and can completely block pore spaces. Based on core permeability data, permeability values in Minas reservoirs are controlled by changes in stratigraphy. The utilization of this approach to get permeability values separately from different stratigraphic intervals will improve understanding of geological relationship within a time-stratigraphic framework.
This paper will discuss approaches to determine a permeability curve based on the support of core-log data and combine with time-stratigraphic marker determination resulting from a detailed sequence stratigraphy study. By using intervals defined by time-stratigraphic markers, core-log transforms could become the best method for determining permeability in old wells, which have no core data. Some transform methods have been tried in this Minas case study i.e: flow zone indicator (FZI), linear, dual and multiple regressions. The multiple regression method yields permeability values, which are in good agreement with core data in Minas clastic sandstone reservoirs.


Authors : Pujiyono & Bambang Poernomo