**Peer Reviewed**

**Source**

**Conference**

**Publisher**

**Theme**

**Author**

**Concept Tag**

- absorption (1)
- absorption cross (1)
- analysis (1)
- aperture (1)
- array (1)
- Artificial Intelligence (2)
- Brine (1)
- channel (1)
- complex reservoir (2)
- composition (1)
- condition (2)
- contribution (1)
- core (2)
- distribution (1)
- Drozdowicz (1)
- experiment (1)
- experimental technique (1)
- fissure (1)
- flow in porous media (1)
- Fluid Dynamics (1)
- formation evaluation (2)
- fracture (3)
- fracture interface wave (1)
- fracture intersection (1)
- fracture plane (1)
- geometry (1)
- hydraulic fracturing (2)
- Influence (1)
- interface (1)
- interface wave (1)
**intersection (4)**- joint (1)
- log analysis (1)
- material (1)
- matrix (1)
- method (1)
- model (1)
- moderator (1)
- network (1)
- percolation (1)
- percolation theory (1)
- permeability (2)
- perpendicular (1)
- polarization (1)
- polyurethane (1)
- porosity (1)
- Reservoir Characterization (3)
- reservoir description and dynamics (4)
- rock (2)
- rock mass (1)
**sample (4)**- seismic processing and interpretation (1)
- shear (1)
- shear wave (1)
- Silicon oxide (1)
- solution (1)
- source (1)
- Source Array (1)
- SPE Reservoir Evaluation (1)
- stress (1)
- structural geology (1)
- surface (1)
- Symposium (1)
- system (1)
- thermal neutron (1)
- transducer (1)
- Upstream Oil & Gas (4)
- variation (1)
- vertical fracture (1)
- void (1)
- vug (1)
- Wave (1)
- well completion (2)
- well logging (1)
- wettability (1)

**File Type**

We performed laboratory experiments on synthetic orthogonal fractures to determine the effect of intersections on fracture interface waves. A seismic array was used to propagate compressional and shear waves along fracture planes as well as along an intersection. Measurements were made for a range of normal stresses (1.4 MPa to 14 MPa). Intersections quench bulk shear waves and produce interface waves independent of the polarization of the shear wave source. Furthermore, these intersection waves are highly sensitive to stress concentrations along the intersection. **INTRODUCTION**

A major difference between working with single fractures and orthogonal fracture networks is the existence of fracture intersections. Fracture intersections enable the formation of three-dimensional dominant flow paths and they act as potential sources of additional seismic wave scattering not observed for single fractures or parallel sets of fractures. A main challenge in working with orthogonal fracture sets is how to determine the connectivity or properties of fracture intersections.

Fracture intersections act as either barriers to flow or paths of high conductivity and are difficult to characterize with non-invasive or destructive measurements. The goal of this study is to determine if the intersection between two fractures exhibited a seismic response that differs from that measured along fracture planes. In this paper, we explore the potential use of fracture interface waves to interrogate the properties of fracture intersections and fractures.

Fracture interface waves are generalized Rayleigh waves that propagate along fractures [1-5]. The existence and velocity of fracture interface waves depend on the normal and shear stiffness of the fracture, and on the polarization of the shear wave. The velocity of these waves ranges from the Rayleigh wave velocity for a free surface to the bulk shear wave velocity for non-effervescent interface wave modes. As mentioned, the existence of fracture interface waves depends on the polarization of the shear components of the excitation source [3], i.e. interface waves exist when the shear-wave polarization is perpendicular to the fracture plane. However, at an intersection, fracture interface waves should always exist for both parallel and perpendicular shear wave polarizations (relative to one of the intersecting fractures) because each component is perpendicular to one of the orthogonal fractures. In this paper, we demonstrate that interface waves along fracture intersections always exist and the waves are sensitive to stress concentrations along the intersection. **EXPERIMENTAL SET-UP** **Samples**

Experiments were performed on aluminum samples measuring approximately 100 mm by 150 mm by 150 mm. Aluminum was used to ensure that the effects observed were from the fractures and not the background matrix. Two samples were used in this study: (1) an intact piece of aluminum that was used as a standard; and (2) a “fracture” sample containing two intersecting fractures (Figure 1). Intersecting fractures in the fracture sample were produced by quartering a solid piece of aluminum. After quartering, the fracture sample was machined to the same external dimensions as the intact specimen. The fracture surfaces were smooth, i.e. no apparent roughness is visible to the naked eye.

array, fracture, fracture interface wave, fracture intersection, fracture plane, hydraulic fracturing, interface, interface wave, intersection, perpendicular, polarization, Reservoir Characterization, reservoir description and dynamics, sample, seismic processing and interpretation, shear, shear wave, source, Source Array, stress, transducer, Upstream Oil & Gas, vertical fracture, Wave, well completion

SPE Disciplines:

**Summary**

Answering general questions such as "Where is the oil?," "How much oil is there?," and "Can we extract it?" is a challenging task for a large fractured field in southern Italy. Various studies were conducted to gain more insight into the way oil is distributed in the rock and the producibility of the different structures observable on the cores (matrix, vugs, and fissures).

These included the cryogenic scanning electron microscope (CryoSEM) and gas chromatography (GC)-pyrolysis, pore-size-distribution measurements, SEM analysis on thin sections, and a number of nonconventional techniques that were designed specifically for that type of rock. Nuclear magnetic resonance (NMR) imaging was conducted on several whole core samples and the different porosity contributions (microporosity, vugs, and fissures) defined on a 3D basis. An analytical approach based on the percolation theory was used to separate the permeability contributions and define the conditions under which vugs and fissures may form a conducting system. The inputs were distributions of pore throats, throat length, coordination number, fissure orientation, and porosities. Wettability is a key parameter for production estimates, and we used a technique for measuring it in both microporosity and fissures, which makes use of dielectric constant measurements. All the data contributed to our current understanding of the reservoir.

analysis, complex reservoir, condition, contribution, core, distribution, fissure, formation evaluation, fracture, intersection, matrix, percolation, percolation theory, permeability, porosity, reservoir description and dynamics, rock, sample, SPE Reservoir Evaluation, system, Upstream Oil & Gas, vug, wettability

ISRM-EUROCK-1993-039

aperture, Artificial Intelligence, channel, complex reservoir, core, experimental technique, flow in porous media, Fluid Dynamics, fracture, geometry, hydraulic fracturing, Influence, intersection, joint, model, network, permeability, polyurethane, Reservoir Characterization, reservoir description and dynamics, rock, rock mass, sample, surface, Upstream Oil & Gas, variation, void, well completion

SPE Disciplines:

- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Naturally-fractured reservoirs (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization (1.00)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (0.92)

Igielski, A. (Henryk Niewodniczaalski Institute of Nuclear Physics) | Woinicka, U. (Henryk Niewodniczaalski Institute of Nuclear Physics) | Czubek, Jan A. (Henryk Niewodniczaalski Institute of Nuclear Physics) | Krynicka-Drozdowicz, E. (Henryk Niewodniczaalski Institute of Nuclear Physics)

The knowledge of the true absorption cross section of thermal neutrons for different rock materials and brines is an important factor in the quantitative interpretation of the neutron lifetime logs. This absorption cross section is directly related to the elemental composition of these materials. Geological materials, however, very often contain some admixtues of highly absorbing isotopes in quantities which are still too low to be detected in the usual elemental analysis (like boron, rare earths, etc. ). The only way to know that cross section is to measure it on geological samples. Due to the particular features of rock material (heterogeneities, impossibility to reproduce the sample of exactly the same composition and bulk density and with different dimensions, etc. ) this is not an easy task using the experimental methods known so far. A new approach to this problem is presented in the paper. In consecutive measurements the rock sample (having a fixed and well known shape - in our case it is a sphere and the sample is powdered or liquid) is enveloped in shells of a Plexiglas moderator (the neutron parameters of which are known) of variable thickness and irradiated with the pulsed beam of fast neutrons. The die-away rate of thermal neutrons escaping from the whole system is measured. The absorption cross section of the sample is found as the intersection of the experimental curve (i. e. die-away rate vs. thickness of the moderator) with the theoretical curve. The theoretical curve is calculated for a given moderator under the assumption of a constant value of the neutron flux inside the sample. This method is independent of the transport cross section of the sample. The method has been checked on artificial materials with a well known elemental composition (liquid or solid) and on the natural brine. For the liquid sample the one standard deviation of the measurement is of the order of 2 or 3 capture units, whereas for the solid sample it is less than 5 capture -units. The volume of the sample needed here is of the order of 1000 ccm.

absorption, absorption cross, Artificial Intelligence, Brine, composition, condition, Drozdowicz, experiment, formation evaluation, intersection, log analysis, material, method, moderator, Reservoir Characterization, reservoir description and dynamics, sample, Silicon oxide, solution, structural geology, Symposium, thermal neutron, Upstream Oil & Gas, well logging

SPE Disciplines:

Thank you!