Intelligent Wireline Formation Tester Evaluation of Low-Permeability and Low-Resistivity-Contrast Formation with Detailed Digital Planning.

Abstract

Exploration and development drilling in offshore China is extending to Paleogene formations that are characterized by low-resistivity-contrast and low-permeability rocks. These formations have become a focus for increasing reserves and production. During exploration activities, these low-resistivity, low-formation-contrast formations have been critical and challenging for formation evaluation because the geological structure and lithology are more complex than in previously discovered fields. Differentiating hydrocarbon from water using petrophysical interpretation has a large uncertainty in these formations. Confirming the fluid type using conventional formation testing technology has been extremely challenging because the produced fluid is mainly mud filtrate, which is of no use for fluid confirmation. The dual-flowline architecture of the intelligent formation testing platform (IFT) is designed to systematically address shortcomings of legacy technology, enabling focused sampling in the tightest conventional formations. Specialized digital planning of the numerical flow models by adding a brine tracking facility and enumeration initialization was performed to (a) compare and benchmark the cleanup performance of conventional radial 3D probe and new focus radial probe; (b) simulate multiple scenarios including hydrocarbon-water transition to understand the salinity changes while pumping in various water saturation circumstance and optimize operational planning by quantifying cleanup time uncertainties even in two-phase fluid reservoir; and (c) history match the sampling drawdown, flow rate, and salinity change with actual sampling data and provide real-time answers to help accelerate the decision-making cycle. This dedicated design resulted in increased efficiency in water sampling compared to previous testing done by the operator. Whereas previous gas-water transition zone sampling was challenging because high water-based mud filtrate fractions masked the presence of formation water and formation hydrocarbon, the focused radial probe, combined with state-of-the-art resistivity measurements and prejob modeling of salinity change, allowed identification of gas and the measurement of formation water resistivity in a multiphase flow environment. The formation testing of these low-resistivity-contrast and low-permeability formations enabled acquisition of a 2% contaminated formation water sample in 140 minutes with formation mobility of 1 md/cP. The gas-water zone was confirmed from a dual-flowline resistivity measurement and a hydrocarbon show in mobility of 1.4 md/cP. The intelligent wireline formation testing platform enabled high-performance and efficient collection and identification of formation water and gas in a low-mobility low-resistivity-low-contrast formation.