Q. Heavy Oil is gaining something of a following amongst oil companies. Has this influenced your decision to commence researching into wireline usage in Heavy oil environments?

A. Actually, we have been involved with heavy oil reservoir measurements and methods for many years. There is no doubt that heavy oil is a special fluid, and it has always been our aim to be able to identify and quantify such fluids for our customers using either wireline or LWD methods. There are certain techniques that we advise our customers to use for heavy oil; it is a different form of oil and we see it as a fundamental aspect of our business.

Q. Are these techniques that you are using in heavy oil environments an adjunct to what you have been doing before, or have they had to be specifically adapted?

A. Both. Some measurements have been adapted to fit the special nature of heavy oil; take, for example, the use of magnetic resonance tools. With our MR Scanner* and CMR-Plus*, unique pulse sequences are in daily use in heavy oil reservoirs. Yet, the solution to some challenges our customers face in heavy oil reservoirs call for new hardware and methods which are part of our ever-developing technology portfolio.

Five technologies quickly come to mind for special consideration in heavy oil: the reservoir saturation tool (RSTPro*) where we use carbon/oxygen techniques; the electromagnetic propagation tool (EPT*) to measure the water filled pore space; magnetic resonance tools (MR Scanner and combined magnetic resonance CMR-Plus); the sidewall core tool; and the pressure and fluid sampler tool. Of course, all of these technologies have applications in traditional light oils, as well as capabilities in quantifying heavy oil and characterizing the reservoirs in which they occur.

Q. How do these tools work, and what do they actually measure?

A. The reservoir saturation tool (RSTPro) can quantify the ratio of carbon-to-oxygen in the formation. In simple terms, water contains no carbon, whilst oil contains both carbon and oxygen, so by achieving a carbon-to-oxygen ratio you can identify and differentiate water from oil. One of the advantages of the RST is that it requires no flow from the reservoir.

The EPT dielectric tool uses a high frequency electromagnetic wave that is primarily affected by water molecules, but not to any great extent by oil molecules. In this way, it will “see” water, whilst formations containing oil or gas remain “invisible”.

The magnetic resonance tools, of which we have several, work by manipulating the protons in fluid molecules. The measurements obtained are either more, or less, effected by the quantity and viscosity of hydrogen-containing fluids in the formation.

Q. How does the sidewall core tool work?

A. The sidewall core tool is a wireline deployed tool that “grabs” a small plug of rock and fluids from the sidewall and carries it to the surface. These cores, nominally 23.4mm in diameter and 50.8mm long, can be obtained by percussion means whereby a hollow bullet is shot into the rock. Alternatively, when the mechanical sidewall coring tool is employed, a small plug is mechanically “cored” out and secreted into a protective sleeve.

Cores are always very useful and although the technology is not considered cutting edge, it is, nevertheless, of huge benefit to have a physical sample which provides such details such as mineralogy and grain size. In addition, these cores also contain fluids. In conventional oil reservoirs, the fluids may have been forced away from the sidewall and deeper into the rock by the drilling mud, and the core method may not reach any “unflushed” rock. However, in heavy oil reservoirs, because the fluid is often virtually immovable, it can still be in place adjacent to the sidewall, and may be “captured” by either the percussion or mechanical method.

However, we do have a pressure sampling and fluid sampling tool, the Modular Dynamics Tester* (MDT), which operates in a number of different ways. One method sets a small packer up against the formation. From the center of the packer, a fluid probe extends out and into the rock and then a small draw-down is instigated in the flow line which sucks a sample of reservoir fluid into a container. The success of this sampling technique depends on the viscosity of the fluid, which may contain not only oil, but also mud filtrate, formation water and gas. Of course, as oil becomes heavier, more viscous, it becomes more difficult to cause fluid to flow. In cased holes, the Cased Hole Dynamics Tester* (CHDT) sets a packer against the casing, then drills a small hole in the casing. When the drilling has gone deep enough to establish pressure communication with the formation, pressure and fluid sampling commences; when the test is completed, a plug may be inserted into the drilled  hole.

Q. What technological challenges are you focusing on?

A. Fluid sampling has limitations if the fluid is too viscous to flow into the tool. However, work is currently underway to combine such a fluid sampling technique with a means of “encouraging” fluid to flow. We will, therefore, be able to provide the client with the ability to flow heavy oil into a wireline sampler.

The technical challenge for the coring tool is the depth we are able to penetrate into the formation. We are currently working to increase this core depth, hopefully to the point that the rock from which the core sample is obtained, will be beyond the zone which has been invaded (and thus contaminated) by fluid from the drilling mud. This development is in direct response to those clients who wish to make a more accurate physical evaluation of what the reservoir holds.

Q. What impact do high-temperature environments and, also, sand production have on your tools and the readings you obtain?

A. Our tools are designed and built for the usual rigors of downhole environments. Specifications to work in temperatures up to 150degC and 175degC are standard.

Sand in production is normally not an issue, since our measurements are generally made while the well is static.

Q. What added-value do your wireline engineers give to the service that customers receive?

A. Our field engineers are the best and brightest folks in the oil patch! They pay great attention to providing our customers with the safest, highest quality service at all times. We also need to acknowledge the worth of Schlumberger petro-technical experts (PTEs)  such as petrophysicists, drilling engineers and geologists, who have local knowledge and experience of their customers’ reservoirs. Not only do they run the synergetic products, but they also provide valuable advice to the customer on what logging they may be considering. They are very much a value-added element for the customer.