Case Studies

Fractured Reservoirs

Understanding Fractures in unconventional and conventional hydrocarbon plays is difficult. In reservoirs where a Dual porosity (DP) system is inherent, it is assumed that both fracture and matrix have storage capacity, the fluid flows from the matrix into the fracture and then from the fracture into the borehole.  However in Dual Porosity-Dual Permeability (DPDP) systems, both the matrix and the fracture are assumed to have storage capacity and fluid transmissivity properties, here the physics of interaction between the matrix and fracture are much more complicated, hence there is a large degree of poorly known variables which may impact the results.

Case Study:

Basement Malaysia

The basement rocks off shore Malaysia are comprised of Metamorphic interbedded sandstone and shale. Exploration is in its infancy and no wells are in production to date.


The Basement rocks in Yemen are igneous and metamorphic rocks mostly Granite, Gabbros, Gneiss & Amphibolite, often targeting the weathered zone at the top of the granite batholith. Basement fields are the major fields in Block-10 East Shabwa (KHARIR Field) in Yemen. This productive block is located in Masila-Say’un Basin, with area of 946 km2. The average daily production of this field is about 35,000 BOPD.

​Red Sea, Egypt

Basement rock reservoirs are located in the Red Sea, Egypt, exploiting the fault and fracture network.

Carbonate Reservoirs

Geode-Energy has worked extensively in carbonate petroleum reservoirs around the world, interpreting a variety of complex petrophysical parameters. Carbonates form a major oil and gas play around the world, however their diverse   depositional environments, texture and pore network contribute to the difficulties of modeling their heterogeneity. Therefore carbonates present us with some of the greatest challenges and require advanced new technologies, if logging acquisition is to be successful.  A number of measurements are key to understanding carbonates. Particularly, facies and their connection to porosity and permeability are fundamental to reservoir characterization.  In addition, fractures can also contribute significantly to production, enhancing permeability through the fracture density, orientation, and aperture.

In this paper, we compare two Carbonate regions both in terms of Geology and logging strategies. The carbonates around Qatar, Saudi and Kuwait are characterized by shallow sea grainstones, forming stacked migrating dunes, whereas in Malaysia and the Philippines, the carbonates were deposited as pinnacle reefs or patch reefs, characterized by stacked coral and coral talus. Karstic development is known to occur at the top of the Pinnacle reef deposits. Both these carbonates are characterized by distinctive facies suites, however most modern interpretation techniques have been developed for Middle Eastern carbonates and may not automatically translate to carbonate reservoirs in South East Asia.  The authors will discuss adapting techniques for combining Image logs, magnetic resonance, and other log data for facies identification and formation evaluation, originally developed for the Middle East, to carbonate buildups found in Malaysia using examples from the region.


Carbonates in Malaysia are characterized by stacked Framework Corals and Coral Talus, dissected by intensive karst development.


The carbonates that form most of the reservoirs in the Philippines are mostly;
-Pinnacle reefs developed on Nido carbonate platforms (e.g. Nido, Matinloc, Cadlao);
-A seaward horst block reef fairway with large pinnacle reefs (Malampaya-Camago trend).


Qatar is characterised by Northfield, Dukhan and Bul-Hanine Fields. The reservoirs are dominated by cross-bedded ooilitic sediments, karst and fractures. Bioturbation can dominate certain facies types


Syrian reservoirs are dominated by Cretaceous dolomite reserviors.


Carbonate oil and gas fields are located in Gulf of Suez in the Ras Fanar Fields in the Nullipore Formation.

Deep Marine Reservoirs

Deep-Water sediments are those sediments deposited below the wave base, on and at the base of the continental slope and transported on to the abyssal plane. The sediments are transported through a number of mechanisms ranging from sediment creep, hyper pycnol flows, turbulence to mass transport deposits. Large quantities of sandstone and shale are remobilized from the shelf in to the deep ocean basins. Sediments can either pool behind topographic barriers forming thick, structureless sandstone, or can travel great distances to form clean, laterally extensive thin beds.

Thin Beds

​The Challenge: Thin bedded turbidites are a very productive play, due to the highly porous, clean laterally extensive beds. However, these beds can be centimetres thick and below the resolution of traditional open-hole logs and therefore only the high resolution borehole images can identify the thin beds. Although, calculating porosity and permeability requires additional processing to sharpen low resolution logs.

Solution: Textures and resistivity contrasts from borehole images, show clear difference between resistive sandstones and conductive shales, critical to sandstone volume calculations. Sharpening neutron and density logs can enhance the resolution to calculate porosity and permeability.

Structureless Sands

The Challenge: Thick accumulations of sands in deep-water settings, require either a large sandy source – such as clean winnowed shelf sands – and sporadic slope failure to mobilise the sand or a continuous supply of sand to the coast over a period of time, either from a fan delta or a major river. Sandstones and other course-grained facies mostly occur in clearly erosive channels and channel complexes that cannibalise previously deposited sands to form large amalgamated bodies. Evidence of the sinuous nature of these channels in planform comes from high quality seismic time slices and varied paleaocurrent directions from dip meter tools.

Solutions: Three-dimensional seismic provides spectacular resolution of turbidite channels, although it is not always clear on seismic whether these channels are mud or sandstone filled? In addition thick mass transport deposits characterized by low acoustic impedance can mask the channel form. Thick bodies of amalgamated, structureless sands are very difficult to correlate laterally on log data, and the lack of flow indicators on borehole image date unhelpful. However, this type of play can contain large reserves if exploited for reserves.

Mass Transport Deposits

Challenge: Mass Transport Deposits (MTD’s) are chaotic often muddy sediments, that form through a variety of processes ranging from slumping, slope creep, to slurry and chaotic, debris flows. Characteristic of these thick beds are shear plane faults, forming multiple ridges. The MTD can form a good reservoir seal to the sandy reservoirs, but can be a drilling hazard due to fault shear reactivation during drilling.

Solution: Based on observations from recent wells drilled offshore Brunei and Sabah, it appears that quiescent sedimentation with thick bodies of conformable bedding planes, with consistent structural dip interspersed with sheet sands and sporadic debris flows form the majority of the deposits. However, enveloping this uniform sedimentary environment, is massive structural failure, involving slides, slumps, and debris flows, followed by post depositional creep. Overlaying these chaotic beds are often thick, massive structural sandstones, possibly suggesting the slope failure is onset by sea level lowering and followed by low stand sandstone deposits.