Abstract

Pressure profile analysis is concerned with the study of systematic variations of formation pore pressure with depth. Formation pore pressures can be directly measured in the subsurface by wireline formation test (WFT) tools which include the RFT, FMT, SFT, MDT, RCI, and RDT. Pressure-depth plots (P-D plots) are the most common interpretation tool used for WFT pressure data, but other techniques that amplify subtle pressure differences are also available. Advances in tool design, metrology, and computer software over the past decade have increased the use and impact of WFT data in exploration, appraisal, and development. The availability of more accurate data has also re-focussed views on potential complexities, as well as on the need for rigorous quality control during both data acquisition and data analysis.

Typical applications of pressure profile analysis include (a) identification of pore fluid type, (b) estimation of pore fluid properties, (c) estimation of fluid contacts and hydrocarbon column heights, (d) quantification of depletion and overpressure, (e) identification of hydrodynamic conditions, and (f) investigation of lateral and vertical reservoir continuity and connectivity. In addition to these applications, WFT data also provide formation permeability estimates, and high resolution borehole temperature information. Interpreted WFT data can provide valuable and cost-effective input on issues such as residual hydrocarbons, fluid contacts, pay identification, trap geometry, seal capacity, reservoir compartmentalization, and reserve estimates. Early use of WFT data and pressure profiles during field appraisal can be particularly leveraging.

Complexities encountered in pressure profile analysis include issues of (a) WFT-derived versus and PVTderived gradients, (b) inter-relation of gradient intersections, free water levels (FWL's), and hydrocarbon-water contacts, (c) abnormal aquifer pressures, hydrodynamics, & perched fluids, (d) supercharging, and (e) integration of WFT and DST data.

Some challenges of working with WFT pressure data include issues of (a) quality control, (b) gauge accuracy and repeatability, (c) systematic gauge errors, (d) subtle seal leakage or probe blockage, (e) choice of appropriate hydrostatic gradients, (f) depth control uncertainty, and (g) error bars and precision.