Abstract
Maintaining and increasing production are the main challenges for oil and gas companies in today's difficult market. To achieve these goals, these companies are looking for new techniques to improve fracture characterization. Open natural fractures, when present, can provide the conduit for the majority of natural gas in low porosity, hard rock environments. Therefore, a complete understanding of fracture attributes is required for optimal production, as well as cementing and completion design, well placement, and reservoir modeling.
In the La Paz field in Venezuela, previous petrophysical interpretation assumed the cementation exponent, m to be equal to 2. This assumption was made due to the absence of special core analysis and logging information such as dipolar sonic and micro resistivity image logs, increasing the uncertainty in the petrophysical model.
Using the crossplot of Ø vs. Rt on log log coordinates it was possible to determine the cement exponent, m, value for each zone. This parameter was fundamental to the estimation of the fracture and matrix porosity, fracture Intensity Index, and the Partitioning Coefficient.
The methodology applied in this case study is based on advanced acoustic analysis integrated with triple combo and borehole micro resistivity images. The triple combo (gamma ray, induction resistivity, neutron and density) and the image data allowed identification of the natural fractures, and the Stoneley wave analysis confirmed that several of the fractures observed in the borehole image data were open.
This methodology reduced the fracture characterization uncertainty of the La Paz Field and helped to more accurately estimate petrophysical properties where special core data is not available.
