Improved Reservoir Characterisation and Management
Malaysia–Thailand Joint Development Area (MTJDA)
One of the more instructive examples of my approach to petrophysics came from the Malaysia–Thailand Joint Development Area, where a major challenge was the recognition of low-resistivity, low-contrast gas pay within complex stacked, freshwater, laminated and convoluted shaly-sand reservoirs.
At the time, partners and potential buyers were unable to recognise the full gas-pay potential from the available routine logs, supplemented in some wells by core and NMR. A reservoir-geological facies scheme already formed the cornerstone of the geological model, so the critical question became simply:
Which facies were reservoir pay, and which were not?
My interpretation differed from the prevailing view. Based on a combination of subtle but consistent responses visible even on routine logs, I concluded that several facies being classified as non-pay were in fact gas-bearing reservoir. Individually, the indicators were easy to dismiss; taken together, they formed a compelling case. This mattered because the disputed facies represented approximately 35% of the gross rock volume under closure.
Rather than relying on interpretation I proposed that we deliberately design the next appraisal well to test the hypothesis. Working with the exploration manager, we targeted the supposedly poor-quality facies for both core acquisition and an isolated production test. I designed a core-analysis and SCAL programme specifically to answer the reservoir questions that mattered: effective hydrocarbon pore volume and gas permeability. Core plugs were selected deliberately across poor, intermediate and better facies to establish a continuous, gradational hard-data reference rather than simply characterising the best reservoir rock.
The objective was broader than proving reserves in a single cored well. The core programme was designed so that the results spe39761.pdfcould subsequently be integrated with routine, inexpensive (routine) wireline logs and applied across uncored wells, without depending upon NMR or resistivity-scanner logs. This integrated methodology became known as Facies-Based Petrophysics.
A bespoke SCAL workflow was developed in which air–brine capillary-pressure behaviour was extended from the SCAL plugs across the entire machine-sampled RCA dataset. Using a tailored J-function approach, capillary-pressure-derived hydrocarbon pore volume could be assigned throughout the cored interval using both porosity and the accurate core measured air permeability, creating a continuous reservoir-quality reference framework.
The final test was crucial. To demonstrate that the disputed facies could produce gas independently, the adjacent better-quality reservoir was first isolated with a squeeze job. The target facies was then flow tested on its own. The dismissed facies flowed approximately 11 MMscf/d.
Petronas subsequently arbitrated and accepted the facies as pay, and the field was awarded an approximately 27% reserves upgrade as a direct consequence of the revised reservoir interpretation.
The work demonstrated an approach that has remained central to my philosophy throughout my career: do not simply process logs using established methods. Identify the geological and reservoir question, recognise where conventional interpretation fails, design the measurements required to test the hypothesis, and integrate core, SCAL, logs, geology and dynamic data into a defensible reservoir model.
The study also established my reputation in the region and subsequently led to a long-term consulting relationship with BP Indonesia. Wan Manan and I documented the work in SPE 39761, which provides considerably more technical detail on this case history.
SPE 39761
LCLRP remains the primary problem of log analysis today and was addressed directly here and used as a templte for future fields worldwide.
Enjoy Petrophysics!