Thinly Bedded Reservoir Study, Application of Sand-Slit-Clay (SSC)-SHARP-Thomas Stieber Juhasz Models, in a Deep Water Field, Offshore Sabah, Malaysia

Abstract

Thinly bedded reservoir study in the deep-water area, offshore Sabah, Malaysia, was performed with the primary objective of improving the understanding of its complex geology. The nature of reservoirs, which are predominantly thin-bed and laminated sandstones of submarine fan environment, contain a high level of uncertainty in its lateral continuity. Standard shaly-sand log analysis methods contribute pessimistic values of porosity and water saturation when applied to these reservoirs. Few techniques are then presented for the determination of these rock properties, which are more reliable with core and production data. Core grain-size analysis of these reservoirs shows that clay content is generally low but the silt content can be significant. Furthermore, log responses show that porosity distribution and mineral-conductivity are influenced mainly by the silt-size particles. A sand-silt-clay (SSC) model was then developed from density-neutron crossplot, which model is also used to determine porosity and water-saturation in addition to volumes of lithology components of the reservoirs. Furthermore, other petrophysical technique, called SHARP, uses 1D convolution filters to match thin bed modelled log curves to their corresponding measured responses. A petrophysical evaluation using standard resolution logs and the thin bed resistivity (SRES) from image response are used to develop a thin bed model that yields high resolution logs. For zones where the resistivity image indicates significant thin bed development, the standard petrophysical analysis should also indicate the existence of free fluid. Although the porosity tools cannot resolve the thin beds, they nevertheless represent the bulk volumetric over the interval, known as Thomas-Stieber-Juhasz (TSJ) method, and would be able to differentiate between porous zones with lower clay volume versus porous shales with high clay volumes. The main point is that if a thin bed interval has some calculated free fluid volume using standard resolution logs, then a thin bed analysis is warranted.

Heterolithic Thin Bedded Reservoirs Volumetric Estimation, Quantification and High-Resolution 3D Modelling

“…Most of the production fields in Malaysia basin and around the globe are from conventional reservoir associated with heterolithic thin bedded (HTB) [1][2][3][4][5][6]. Heterolithic Reservoir description depending on scale of thin bedded, heterogeneous, or laminated pay, which refer to the formation with two or more sand members that non-communicating, each probably with distinct relative and specific permeability characteristics as explain by Henderson et al, [7], Kantaatmadja et al., [9], Nayagawa et al, [12], Stromberg et al, [15]. The HTB is refer to permeable beds interbedded with impermeable shales bedded with millimeter (mm) to centimeter (cm) thickness, which is below standard log resolution and commonly associated with conventional reservoirs.…”

Designing a pragmatic solution for complex numerical modeling problem in thinly laminated reservoirs

“…Even if the petrophysical advanced tools and algorithms could distinguish the commercial thin bedded hydrocarbon bearing zones (Onn et al 2016) and enhance the vertical resolution of logs (Kantaatmadja et al 2015) to the centimeter scale for proper volumetric calculations, the numerical modeling of this type of reservoirs for successful dynamic reservoir simulation and production forecasting, would still remain a challenge. For a full field simulation study of thin bedded sands of vertical resolutions of around 2-5 cm, building a high resolution reservoir model, simply results in a multi-hundred million cell model.…”