SPWLA Kuwait 2007/2008

   May - 2008

Borehole Resistivity Images A powerful Tool for Reservoir Architecture Modeling

M.A Abdel Fattah
RES, Halliburton, Cairo, Egypt

This presentation highlights the value of borehole image logs for reservoir characterization, particularly when fully integrated with core and seismic data. Some implications for reservoir model construction are also emphasized. It presents the applications of resistivity images in enhancing reservoir evaluation through detailed structural and sedimentological interpretation.

Structural interpretation includes defining structural dip zones and any angular unconformities. It is important tool in identifying the orientation of faults and fractures as well as the present-day tectonic stress field orientation from drilling induced features.

Sedimentary dip types were used in order to define lithofacies, depositional packages based on lithofacies association and to determine palaeoslope and palaeocurrent orientations.

The images have added finer scale detail to the vertical facies succession and stratigraphic dip changes, and have enabled the identification of significant depositional surfaces. Finally, the recognized depositional packages are interpreted in terms of an overall depositional model.

Correlation based mainly on the image sedimentological facies analysis is an approach for high resolution reservoir anatomy to clarify the lateral facies changes and consequently to solve many problems related to the reservoir geometry and shed light on reservoir connectivity.

   April - 2008


SPWLA Kuwait
April 29th, 7:00PM at Al Manshar Rotana Hotel, Fahaheel

Presented by
Jannes Kloos, Log Analyst, Baker Atlas

The Coates and SDR models for deriving permeability from NMR T2 distribution data are based primarily on pore-body sizes and are thus more valid for rocks where a good correlation between pore-body-size to pore-throat-size exists - a characteristic not observed in many carbonate rocks. In this presentation, we show a modified Coates permeability model which takes into account the pore connectivity in carbonates. This model is applicable not only for vuggy carbonates but also to formation rocks that contain abundant mud and/or intragranular porosities.

We have used (DiRosa et al., 2006) simple approach of generalizing the Coates equation by introducing a pore connectivity coefficient. By that we achieve a remarkable fit to core data.

Examples and case histories from the Middle East are shown that use core, formation multi-test, or image data to estimate the pore connectivity parameter and consequently, improve the accuracy of permeability estimation for complex carbonate formations where multiple facies are present.

About the presenter:

Jannes has 15 years of oil industry experience, 13 of which with Baker Atlas, in openhole logging technologies, formation evaluation, core logging and borehole image interpretation. He has extensive experience with borehole image interpretation projects from Africa, Europe, Russia and Middle East. He holds an M.Sc. in Earth Sciences from the University of Utrecht (1991, The Netherlands) with a major in Structural Geology. He is member of the SPE and SPWLA.

   March - 2008

Effect of Resistive Invasion on Resistivity Logs Presented by Steve Crary Wireline Domain Champion Saudi Arabia

One of the more difficult decisions facing the petrophysicist is deciding which resistivity tool to use. Induction tools are best in low-resistivity formations (fresh or nonconductive muds). Laterolog or resistivity tools are best in the opposite conditions. An important effect to consider when choosing the tool is the contrast of flushed zone resistivity (Rxo) to formation resistivity (Rt). Resistivity tools have a difficult time estimating true formation resistivity when Rxo is greater than Rt. This effect, though well known, still seems to catch petrophysicists by surprise and causes serious errors in the formation analysis. In this paper we demonstrate the potential problems by examining three case studies where both induction and resistivity tools were run and comparing tool response to forward modeling results to help explain the readings.

The first case study could be considered a classic case of resistive invasion. The mud resistivity was 0.78 ohm-m at bottomhole temperature. In a wet sand, the deep resistivity measurement is affected by the higher flushed zone resistivity and consequently reads much higher than the deep induction measurement. The resistive invasion is clearly seen on either the resistivity or induction measurements and can therefore be detected, although it is easier to estimate Rt with the induction. Resistive invasion effects are much more difficult to see on our second case study. A fractured carbonate with high formation resistivity of around 100 ohm-m was drilled with fresh mud. The fresh mud invasion in a wet zone results in Rxo greater than Rt and the deep resistivity was consequently higher than the deep induction by almost one decade. However, the natural fractures resulted in the deep resistivity reading being greater than the shallow resistivity, which is typical of pay zones, and made detection of the shallow resistive invasion difficult using only a deep and shallow resistivity. Forward modeling suggests that the deep induction provides the best estimate of Rt in wet zones, while the deep resistivity measurement is best in hydrocarbon intervals. The final case study demonstrates this effect on a resistivity measurement made while drilling. The measurement was to be used to stop drilling at the top of a water leg. Unfortunately, the fresh mud filtrate and rapid spurt resulted in a flushed zone resistivity higher than formation receptivity in the water leg. Comparison between the bit resistivity (earliest measurement on the tool) and later measurements provided an indication of the effect. However, the difference is subtle and difficult to see on the field logs. Again, comparisons with the induction data clearly demonstate the limitations of resistivity measurement in this environment.

About the presenter:

Steve F. Crary is currently the Schlumberger Wireline Domain Champion in Saudi Arabia. He joined Schlumberger as a Field Engineer in Monahans Texas in 1975, after graduating from Purdue University with a degree in Physics. Beginning in 1980, he held various sales and management positions in Texas, Calgary Canada and New Orleans, Louisiana until August 1997 when he transferred to Schlumberger's Sugar Land Product Center as Petrophysical Expert for the Magnetic Resonance Department. He transferred to Moscow Russia in January of 2002, and Saudi Arabia in 2005. He has published many papers on different aspects of Formation Evaluation, and is a member of SPE, SPWLA, and SE