Unlock Hydrocarbon Volumetric Potential of LRLC Clastic Reservoirs in Malaysian Basins
Authors: Kantaatmadja Budi , Nurhono Achmad Aprayoga , Bt. A. Majid Rosemawati , Bt. Mohamad Noriani Yati , B. Amdan Amri 
Published: March 2015

Low resistivity low contrast (LRLC) pays/intervals mostly are being examined via behind casing analysis and produced thru production enhancement works from idle wells in numerous oil fields in Malaysian Basin. However, with the aim of unlocking hydrocarbon volumetric LRLC potential, it should include seismic data analysis in addition to formation analysis behind casing. In the past, these LRLC intervals were often ignored and considered as water-wet sands due to high water saturation or as tight sands. These intervals, which contain significant reserves, have been recognized and presented in several technical papers explaining its appropriate identification and evaluation techniques using well-data (logs and samples/cores).

The economic importance of LRLC pay sands in the Malaysian Basin has just recently been demonstrated. These pays may lead to a large areal extent and may contain ten to hundred millions barrels of hydrocarbons. The integration and proper techniques of petrophysics and geophysics may become a vital approach for understanding the hydrocarbon distribution (volumetric) within a large areal extent.

The possible environment of depositional for developing LRLC reservoirs are: 1) deep water fans including MTD (mass transport deposit), 2) turbidites, 3) shoreface (middle to lower part), 4) delta complex (i.e. delta front and toe deposits), and 5) channel fills. The LRLC may not occurred in alluvial fans and aeolian deposits. These 5 environment of depositions may accumulate several types of LRLC sediments such as: laminated intervals; bioturbated intervals (with dispersed and/or structural clays); altered framework grains and/or smaller grain size (i.e. silty sand reservoir). The thinly laminated sand is probably the most significant reservoir in term of producing hydrocarbon comparing to the other LRLC types.

The understanding of logging tools (wireline, LWD) and its responses can be used to build petrophysical and rock-physic models that can evaluate these LRLC reservoirs. But having available advanced logs such as NMR, Image, sonic (Vp and Vs) logs, it is a plus for a better analysis. Furthermore, an elastic property (rock physics) from seismic data may establish a clear separation for different lithology and fluid saturation on LRLC sands and may lead to future recommendation work on LRLC reservoir characterization.

The objective of this paper is to provide the above understanding with explanation and examples.

Introduction

In Malaysia basins, the LRLC (Low Resisitivity Low Contrast) sands are being recognized and brought into production recently. Previously, these sands were considered negligible in term of its commercial; but now, it has enough evidence confirming by available well-data that these sands are of economic importance.

With occurrences of numerous productive intervals have been indentified, it encourages us on understanding further on its geologic background, depositional scheme, geophysic assessment, and proper formation evaluation from available well-data such as well-logs, cores, and production history.