Integrated Formation Evaluation and Testing Techniques for Ultra-Tight Reservoirs

Abstract As exploration wells are drilled deeper, low-permeability reservoirs are increasingly encountered. Accurate evaluation of such tight reservoirs has significant commercial implications because operators must demonstrate the presence of sufficient reserves and producibility to justify moving to field development. However, this decision poses many challenges to current workflows. This paper will present and demonstrate the use of integrated formation evaluation approaches based on two different prospects in Southeast Asia, both featuring clastic formations with low-to ultralow permeability. In both cases, specialized, comprehensive logging evaluation programs, which integrate petrophysics, geology, downhole testing, and acoustic data, are designed to quantify key rock parameters, including porofluid and lithofacies distribution, saturations, and permeability estimation at reservoir conditions. The petrophysics logs are analysed near real time to help optimize subsequent downhole testing and coring acquisition runs. Different formation testers are then deployed for these two wells to obtain formation pressure, assess mobility and permeability, and collect high-quality fluid samples. The workflow that enables achieving logging objectives through effective operations is presented in detail. This paper will contain real time log evaluations using actual field data, exhibiting advanced logging technologies including nuclear magnetic resonance (NMR), elemental spectroscopy, dielectric dispersion, image logs, and downhole formation testers. The integrated analysis of data provided by these technologies helps to characterize rock quality and calculate reserves within the critical operational time frame. Different workflows are used to provide petrophysical inputs for formation tester (FT) and drillstem test (DST) selection and interpretation. Fit-for-purpose workflows designed to extract detailed reservoir information, including rock and fluid volumes, porosity, saturation, free fluid, gas-corrected porosity, permeability, calibrated permeability, producibility, net thickness, rock facies, and rock typing, will be presented. This paper will also address formation testing challenges, particularly for low-to ultralow permeability reservoirs. Key considerations include selecting an efficient inlet geometry and area to connect the formation tester to the sand face. Once connected, ultralow-rate pumps are required to minimize sand face pressure decrease and maintain single-phase flowing reservoir fluids. Additionally, a new intelligent wireline FT platform equipped with an advanced downhole fluid analyzer (DFA) will be introduced. Downhole measurements include reservoir fluid composition (including CO2), saturation pressure, fluid compressibility, density, and viscosity. These data are used to generate an equation of state (EoS). The effectiveness of the logs-based integrated approach is illustrated by examples from two distinct prospects in the Southeast Asia region. This approach will explore lessons learned and best practices essential for achieving all the logging and testing objectives, even under challenging reservoir conditions. The discussion aims to provide valuable insights and methodologies, which can be adapted and applied to similar conditions in other regions of the world, enhancing overall efficiency and accuracy of information from evaluation and testing processes.