Reservoir Crude Oil Viscosity Estimation From Wireline NMR Measurements - Rajasthan, India

Abstract

In 2004, the Mangala, Aishwariya, and Bhagyam fields were discovered in Rajasthan, India. In these high-permeability paraffinic reservoirs, viscosity is one of the main factors controlling performance. Pressure, volume, and temperature (PVT) data show areal and vertical variations in crude properties. Meter-by-meter geochemical core analyses corroborate vertical variations in oil composition. Continuous wireline measurements of nuclear magnetic resonance (NMR) properties and station NMR properties from wells drilled with both water-based muds (WBM) and synthetic oil-based muds (OBM) were also used to calculate a viscosity profile. This paper correlates results from all techniques and shows how NMR measurements can provide oil viscosity profiles in compositionally complex pools.Black-oil PVT samples typically test several meters of reservoir, while Rajasthan geochemical data are available at meter scale. NMR logs provide continuous data, and calibrated to PVT and geochemistry, they can provide the most detailed picture of in-situ viscosity variations.Results were used to construct a detailed spatial description of the reservoir's in-situ oil viscosity. The NMR data helped to define a zone of biodegraded oil up to ∼25 m thick above the oil-water contact (OWC) and showed thin accumulations of higher-viscosity oil on top of minor shale layers within oil columns. The major conclusion is that detailed in-situ oil viscosity profiles can be developed from conventional wireline T2 measurements.

Production

“…Further suggestions involve the use of composite cables and coiled tubing operations as well as increasing the lubrication length to extend the capabilities of wireline tools (Zittel et al, 2006). Recognizing that wireline intervention may cut the cost by as much as 50% in comparison with conventional rig operations, several qualification campaigns have been carried out.…”

Evaluation of the hydrocarbon source rock and the reservoir characterization of the Minagish Formation using wireline logs

“…The upper part lithofacies is mainly peloidal wackestones-grainstones, packstone, and mudstone. The reservoir has been suggested to be heterogeneous because of the rapid decline pressure of many wells that have been tested to date, with relatively low productivity ( Thomas, 2007 ; Zittel et al., 2008 ).

Figure 1 A) A) Map showing the location of the Umm Gudair oil field in Kuwait, B) Base map showing the location of the wells that have been used in this study.

…”