J.A.M. Kenter

Acoustic properties of carbonates: Effects of rock texture and implications for fluid substitution

More than 250 plugs from outcrops and three nearby boreholes in an undisturbed reef of Miocene (Tortonian) age were quantitatively analyzed for texture, mineralogy, and acoustic properties. We measured the P- and S-waves of carbonate rocks under dry (humidified) and brine-saturated conditions at 10 MPa effective pressure with an ultrasonic pulse transmission technique (1 MHz) . The data set was compared with an extensive database of petrophysical measurements of a variety of rock types encountered in carbonate sedimentary sequences. Two major textural groups were distinguished on the basis of trends in plots of compressional-wave velocity versus Poisson’s ratio (a specific ratio of P-wave over S-wave velocity). In granular rocks, the framework of depositional grains is the main medium for acoustic-wave propagation; in crystalline rocks, this medium is provided by a framework of interlocking crystals formed during diagenesis. Rock textures are connected to primary depositionalparameters and a diagenetic ov...

Carbonate petrophysical rock typing: integrating geological attributes and petrophysical properties while linking with dynamic behaviour

Abstract Carbonate rock typing provides a vehicle to propagate petrophysical properties through association with geological attributes and, therefore, is critical for distributing reservoir properties, such as permeability and water saturation, in the reservoir model. The conventional approaches to rock typing have significant gaps in incorporating diagenetic processes, transferring rock types from core to log domain, accounting for fractures and using appropriate methodology to realistically distribute rock types in the static reservoir model. The workflow proposed in this paper addresses these issues in a comprehensive way by determination of petrophysical rock types (PRTs), which control static properties and dynamic behaviour of the reservoir, while optimally linking to geological attributes (depositional and diagenetic) and their spatial interrelationships and trends. This approach is novel for the fact that it: (1) integrates geological processes, petrophysics and Earth modelling aspects of rock typing; (2) integrates core and log scales; and (3) provides a flexible ‘road map’ from core to 3D model for variable data scenarios that can be updated with progressive changes in data quality and quantity during the life cycle of an asset. This paper introduces the rationale behind this workflow, and demonstrates its workings and agility through deployment in two large carbonate fields.

Acoustic behavior of sedimentary rocks: Geologic properties versus Poisson's ratios

Velocity transforms are essential for the extraction of geologic information from seismic reflection data sets and/or predicting porosity from wireline logging data. Most commonly used transforms, like the Wyllie time average equation, the Raymer modified time-average equation, and the Gardner equation are all based on empirical relationships extracted from relatively small, “clean” mono- and bimineral and mostly siliciclastic data sets and generally fail to explain the acoustic relationships within multimineral data sets. To extract globally significant relationships between geologic and acoustic parameters, more than 2800 plug measurements were collected. More than two-thirds of the data were our own measurements; the others were from the literature. This data set covers nearly all sedimentary environments and mixtures of those as well as the entire range in petrophysical properties.

Tengiz Field (Republic of Kazakhstan) Unit 1 Platform Static Model: Using a Hybrid Depositional - Diagenetic Approach

Traditional rock typing combined with an inferred depositional linkage for variogram-based simulation is a standard approach in carbonates. In the Tengiz Unit 1 platform, reservoir properties of carbonates as defined by Petrophysical Rock Types (PRTs) are the product of primary depositional facies and diagenetic modification that have separate spatial trends and interactions. Careful, multidisciplinary and targeted analysis is required to unravel such trends from the usually complex hard data sets, but is critical as an understanding of the trends forms the basis for reservoir modeling of the Tengiz Unit 1 platform. Depositional cycles in the Unit 1 Tengiz platform (Late Visean to Bashkirian) are made up of a succession of generally shoaling lithofacies overlying a sharp base with evidence for subaerial exposure and/or flooding. Systematic study of the diagenetic products of several sequences across the platform using petrography, stable isotopes and CL revealed that the diagenetic modification includes early meteoric dissolution and subsequent cementation, late burial dissolution and late burial bitumen cementation.. PRTs are designed to include spatial attributes of the combined stratigraphic, facies and diagenetic framework form the basis for the Multiple Point Statistics and Facies Distribution Modeling (MPS/FDM) simulation of the SIM08T Unit 1 static platform reservoir model. Of the six PRTs, one is linked to volcanic ash (PRT 1), one associated with bitumen (PRT 2) and four with increasing porosity (PRTs 3-6) where PRT 3 tight and PRTs 4-6 represent increasing reservoir quality with PRT 6 the highest quality. PRT maps and a vertical proportion curve were used to generate the facies probability cube and convolved with training images, specifying the spatial interrelationship, to generate a PRT realization. The revised sequence stratigraphic framework and integration of novel concepts in modeling the diagenetic overprint addressed the need for a refined understanding of the platform in preparation for the FGP miscible gas injection project. In addition, the extensive use of MPS/FDM modeling approaches in Unit 1 has resulted in a more realistic integration of both depositional and diagenetic trends in the Unit 1 platform.