Joan Embleton

VP/VS characterization of a heavy-oil reservoir

This article demonstrates a VP/VS application for a heavy oil field near Plover Lake, Saskatchewan, where Nexen has applied both hot and cold production methods. Plover Lake Field is about 8 km east of the Alberta-Saskatchewan border and about 320 km north of the Canada-U.S. border. Oil sands of the Devonian-Mississippian Bakken Formation are found in NE-SW trending shelf-sand tidal ridges that can be up to 30 m thick, 5 km wide, and 50 km long. Overlying Upper Bakken shales are preferentially preserved between sand ridges. The Bakken Formation is disconformably overlain by Lodgepole Formation carbonates (Mississippian) and/or clastics of the Lower Cretaceous Mannville group. Since sandstones have larger S-wave velocities (and hence lower VP/VS ratios) than shales, VP/VS maps should help to identify thickening sand layers within the target zone. We also intend to examine changes within the reservoir due to cold production. Unlike the steam injection processes used in enhanced heavy oil recovery, cold prod...

Seismic pursuit of wormholes

Cold production has become increasingly popular in the extraction of heavy oil, due to the development and widespread use of progressing cavity pumps—essentially powerful augers that suck both oil and sand into the well. At the onset of production, these pumps produce about 60% oil and 40% sand. However, production can improve to 95% oil with only 5% sand after a few months. This increase in oil production and reduction in sand production is attributed to the development of high-porosity tubes termed “wormholes.” Roche (2002) describes wormhole development as the creation of a network of “horizontal wells without using a drilling rig.” Operators who plan infill drilling rely on wormhole distribution information to optimize well spacing. It is accepted that aggressive cold production of oil sands will increase oil recovery, and this has been demonstrated in several pools, both in Alberta and Saskatchewan. So, assuming these induced sand channels can boost cold heavy oil production, can we map them? Thats a good question because wormholes have small dimensions compared to seismic wavelengths, making their seismic detection extremely difficult. This challenge caused us to perform feasibility tests based on a number of models from the literature. The following describes the results of these tests. We also show some real seismic data with promising indications for wormhole imaging. Much heavy oil recovery in Western Canada involves steam injection. Time-lapse seismology plays a major role in monitoring steam fronts and time-lapse or “4D seismology” is now a standard reservoir characterization tool. However, steam production/injection is costly, and heavy oil production now increasingly uses cold flow techniques. As stated earlier, cold production methods use special pumps, known as progressing cavity pumps (Figure 1). These pumps, similar to an auger or “Archimedes screw” within a flexible sleeve, lift the oil/sand mixtures from the producing formation …

Collaborative methods in enhanced cold heavy oil production

Heavy oil reservoirs are an abundant hydrocarbon resource, which will in all probability comprise a significant portion of long-term world oil production. The worlds heavy oil reserves have been estimated to be about 6 trillion barrels—roughly equivalent to conventional reserves. The largest heavy oil reserves are in Canada, Venezuela, the United States, Norway, Indonesia, China, Russia, and Kuwait.

Synthetic core from conventional logs: A new method of interpretation for identification of key reservoir properties

We developed a unique method to generate reservoir attributes by creating an artificial core for those wells that have no core, but that have gamma, neutron, and density logs. We examined sedimentary facies distributions, reservoir attributes, and mechanical parameters of the rock for noncored wells to increase the data density and improve the understanding of the reservoir. This method eventually helps to improve high-resolution 3D geocellular models, geomechanical models, and reservoir simulation in reservoir characterization. Artificial or synthetic cores are created using a single curve that builds facies templates using the information from the cores of nearby offset wells, which belong to the same depositional environment. The single curve, called the fine particle volume (FPV), is the average of two shale volumes calculated from the gamma-ray log and from a combination of neutron and density logs. Using facies templates, the FPV curve builds the synthetic core for geocellular modeling and reservoir simulation, and it represents the sedimentary facies distribution in the well with all the reservoir attributes obtained from laboratory data of the original core. The vertical succession of the synthetic core has the characteristics of actual sedimentary facies with reservoir attributes such as porosity, permeability, and other rock properties. The result of creating the synthetic core was validated visually and statistically with the actual cores, and each of the cored wells was considered as a noncored well. The limitation of this method is associated with the accuracy of the logging data acquisition, normalization factors, and facies template selection criteria.

Time-lapse seismic analysis of a heavy oil cold production field, Lloydminster, Western Canada

Alberta, Canada has enormous heavy oil deposits, which represent the majority of Canada’s future oil reserves. In heavy oil recovery, cold production is less expensive than steam drive methods and has become more popular due to the development and widespread use of progressive cavity pumps (Lines at al., 2003). The distribution of “wormholes” formed during cold production is a major concern for reservoir engineers. Through their modeling work, Lines et al. (2003) have concluded that the resolution of individual wormholes is almost impossible using the normal surface seismic frequency range. However, they suggested that it should be possible to detect the presence of wormhole zones. Figure 1: Locations of the two time-lapse 3D seismic surveys.

The resolution and detection of “subseismic” high-permeability zones in petroleum reservoirs

In petroleum reservoir characterization, it is essential to delineate zones of high permeability that affect production. In this study, we examine the resolution and detection of permeable conduits that are important in production of heavy oil from bituminous sands and the production of gas from fractured carbonates.

The effects of cold production on seismic response

Cold production is a nonthermal recovery mechanism in which a progressive cavity pump simultaneously produces oil, water, gas, and sand.

Detecting "subseismic Features" In Time-lapse Seismology: Feasibility Studies For Fractures And Wormholes In Producing Reservoirs

A variety of geological features in petroleum reservoirs, which affect production, are associated with zones of high permeability. As these regions are composed of distributions, seismic delineation of individual high permeability conduits is difficult, if not impossible. The reason for this is that individual production channels are below the resolution limits of seismic data acquisition, that is, they have dimensions less than typical seismic wavelengths. However, the distributions, which include fractures in standard reservoirs and wormholes in heavy oil production wells, will display a detectable seismic signature when a differencing of seismic data similarly acquired at various time intervals. This time-lapse acquisition approach, followed by the differencing of the two data, produces what has been termed the seismic footprint. Information regarding the reservoir’s spatial development, as well as indicators for future drilling, may be inferred from these footprints. Here, modeling and real data examples illustrate the seismic effects of sub-seismic high permeability zones.

Cold production footprints of heavy oil on time-lapse seismology: Lloydminster field, Alberta

The simultaneous extraction of oil and sand during the cold production of heavy oil generates high permeability channels termed as “wormholes”. The development of wormholes causes reservoir pressure decrease below the bubble point, resulting in dissolved gas out of solution to form foamy oil. The foamy oil could fill depressurized drainage regions (production footprints) around the borehole, leading to fluid phase changes. In this paper, the upper bound and lower bound models on the fluid mixture bulk moduli have been used to detect the sensitivity of seismic P-wave velocity. Then the Gassmann Equation has been employed to calculate the bulk modulus variations of the drainage rocks, where the velocity and density decrease dramatically due to some exolved gas. A 2D cold production model has been built to examine the seismic responses of drainage regions based on well logs in the Lloydminster cold production pool. The seismic modelling responses indicate amplitude anomalies and traveltime delays in these regions upon comparison of pre and post production results. However, because most heavy oil cold production reservoirs are very thin, with less than 10 m of net pay, seismic resolution is a challenge. Different seismic frequency bandwidths have also been tested to look at how vertical seismic resolution determines the detection of the drainage regions.

Interpretation of geologic facies in seismic volume using key rock elastic properties and high-definition facies templates

AbstractWe have developed a deterministic workflow in mapping the small-scale (centimeter level) subseismic geologic facies and reservoir properties from conventional poststack seismic data. The workflow integrated multiscale (micrometer to kilometer level) data to estimate rock properties such as porosity, permeability, and grain size from the core data; effective porosity, resistivity, and fluid saturations using petrophysical analyses from the log data; and rock elastic properties from the log and poststack seismic data. Rock properties, such as incompressibility (lambda), rigidity (mu), and density (rho) are linked to the fine-particle-volume (FPV) ranges of different facies templates. High-definition facies templates were used in building the high-resolution (centimeter level) near-wellbore images. Facies distribution and reservoir properties between the wells were extracted and mapped from the FPV data volume built from the poststack seismic volume. Our study focused on the heavy oil-bearing Cretace...