Luca Duranti

Three-dimensional pore networks and transport properties of a shale gas formation determined from focused ion beam serial imaging

Three-dimensional pore network reconstructions of mudstone properties are made using dual focused ion beam-scanning electron microscopy (FIB-SEM). Samples of Jurassic Haynesville Formation mudstone are examined with FIB-SEM and image analysis to determine pore properties, topology, and tortuosity. Resolvable pore morphologies (>~10 nm) include large slit-like pores between clay aggregates and smaller pores in strain shadows surrounding larger clastic grains. Mercury injection capillary pressure (MICP) data suggest a dominant 1–10 nm or less size of pores barely resolvable by FIB-SEM imaging. Computational fluid dynamics modelling is used to calculate single phase permeability of the larger pore networks on the order of a few nanodarcys (which compare favourably with core-scale permeability tests). This suggests a pore hierarchy wherein permeability may be limited by connected networks of inter-aggregate pores larger than about 20 nm, while MICP results reflect smaller connected networks of pores residing ...

Inverting for reservoir pressure change using time-lapse time strain: Application to Genesis Field, Gulf of Mexico

There are increasing numbers of published examples from around the world in which significant 4D time shifts have been observed in the overburden above producing reservoirs.

4D time strain and the seismic signature of geomechanical compaction at Genesis

Genesis Field, which lies in the Green Canyon area of the Gulf of Mexico at a water depth of 790 m, consists of a series of unconsolidated Pleistocene/Pliocene-aged turbidite sands, dipping up against a salt-cored ridge. Since first oil in 1999, the field has been under primary production, and, although there is a moderate natural water drive in parts of the field, much of it has undergone significant compaction resulting from pressure depletion. The compaction has had severe economic ramifications, as recently several wells have been lost due to compaction-related shear failure.

DISPERSIVE AND ATTENUATIVE NATURE OF SHALES: MULTISCALE AND MULTIFREQUENCY OBSERVATIONS

SUMMARY Intrinsic dispersion and attenuation of shales is investigated by means of multiscale and multifrequency measurements acquired on a West African shale. Results show that shales may exhibit dispersion and attenuation peaks in spite of the very low permeability. The observed frequency dependent behavior of the elastic parameters of shales has a primary impact in the sonic to ultrasonic band, while it is roughly constant for seismic frequencies. The multiscale and multifrequency nature of the investigation, which measures variable volumes of shales, indicates that shales are homogeneous albeit dispersive materials.

Stress-induced velocity anisotropy measurements in unconsolidated sand using a phased-array uniaxial compaction cell

Summary An experimental device for measuring the transverse isotropic (TI) elastic properties of sediments unde r uniaxial strain conditions has been developed. The phased array compaction cell utilizes matched sets of P- and S-wave ultrasonic transducers located along the sides of t he sample and an ultrasonic P-wave phased array source with pinducer receiver on the ends of the sample. The p hased array provides plane P-waves that are used to measu re phase velocities over a range of angles. From thes e measurements, the five elastic constants for TI med ia can be recovered as the sediment is compacted, without the need for sample unloading or reorienting. Descripti ons of the apparatus and data processing and an applicatio n to an unconsolidated sand sample are provided in this pap er. Pwave anisotropy of 20% has been observed in dry sand under an axial stress of 5 MPa.

Phased array compaction cell for measurement of the transversely isotropic elastic properties of compacting sediments

Phased array compaction cell for measurement of the transversely isotropic elastic properties of compacting sediments Kurt T. Nihei 1 , Seiji Nakagawa 2 , Frederic Reverdy 3 , Larry R. Myer 2 , Luca Duranti 4 , and Greg Ball 4 ABSTRACT Sediments undergoing compaction exhibit transversely isotropic (TI) elastic properties that are described by five elastic constants. Continuous determination of all five constants in the laboratory during compaction is a difficult task. In this paper, we present a new experimental apparatus, the phased array compaction cell, for measuring the TI elastic properties of clay-rich sediments under uniaxial strain consolidation conditions. This apparatus uses matched sets of P- and S-wave ultrasonic transducers located along the sides of the sample and an ultrasonic P-wave phased array source together with a miniature P-wave receiver on the top and bottom ends of the sample. The phased array provides plane P-waves that are used to measure phase velocities over a range of angles. From these measurements, the five TI elastic constants can be recovered as the sediment is compacted, without the need for sample unloading, re-coring, or reorienting. Descriptions of the apparatus, data processing and an application demonstrating recovery of the evolving TI properties of a compacting marine sediment sample are provided in this paper. Formerly Lawrence Berkeley National Laboratory, California, U.S.A.; presently Chevron ETC, California, U.S.A. Email: knih@chevron.com. Lawrence Berkeley National Laboratory, California, U.S.A. Email: snakagawa@lbl.gov. Formerly Lawrence Berkeley National Laboratory, California, U.S.A.; presently CEA, Gif sur Yvette, France. Email: frederic.reverdy@cea.fr. Chevron ETC, California, U.S.A. Email: ludu@chevron.com; bagj@chevron.com. INTRODUCTION Anisotropy in the overlying reservoir strata, when left uncorrected for, can detrimentally affect efforts to image reservoir structure and estimate reservoir properties using seismic methods. While clay-rich rocks often constitute the major fraction of sedimentary basins, only a

Inverting for Pressure Using Time-Lapse Time-Strain – Application to a Compacting GOM Reservoir

A028 Inverting Strain – Application for Pressure to Using a Compacting Time-Lapse GOMTime- Reservoir N. L. Duranti Hodgson* (Chevron (Heriot-Watt ETC) J. University) Rickett (Chevron C. MacBeth ETC) (Heriot-Watt & K. Nihei (Chevron University) ETC) SUMMARY Quantitative estimation of dynamic reservoir properties from time-lapse seismic is becoming increasingly widespread. In compacting reservoirs however the 4D seismic signal is complex due to stress and strain redistribution in reservoir and non-reservoir rocks. Several authors have reported observing measurable time-shifts in the overburden on time-lapse seismic data. A method for using these overburden time-lapse time-shifts to invert for reservoir pressure change is presented.