Sophisticated Core Technology

Kevin Dennis, a manager at DTK Group, is optimistic about the demand for core analysis in the Mexican market today. “Right now, Pemex probably has the same level of drilling activity as it did in the 1990s. However, we estimate that the market for core analysis and other sample studies has increased around 300% since that time, showing that Pemex is now placing more importance on these types of measurements, and conducting these activities more and more as a result. Pemex used to take around one or two cores per well, whereas now it is standard for the company to take six to eight cores. In recent years, Pemex has taken as many as 18 to 20 cores.”

Core analysis – the assessment of cylindrical samples of reservoir rocks in a laboratory – not only helps operators make critical decisions based on the quality of the hydrocarbon system, but also enables them to get maximum productivity out of their wells, for example by showing where horizontal wells should be drilled instead of vertical wells.

When asked about the role sophisticated core analysis can play in enhanced oil recovery processes currently ongoing in Mexico, Dennis is keen to stress that the first priority for Pemex at its mature offshore fields of Cantarell and KMZ is to determine exactly how much oil is left. Sophisticated core analysis can assist in determining how much fluid is left in a reservoir and how it is distributed. In secondary recovery processes such as CO2 injection, core analysis can be used to predict whether the cost of an injection programme is economically viable.

Sophisticated core analysis earns its name from simulating reservoir conditions in the lab in order to better analyse the samples and provide more information about the well from which the samples have been taken. “The equipment is fairly sophisticated,” explains Dennis, “because you need to be monitoring saturations continuously during the testing, which means using X-rays, tomography or some type of gamma system that tells you in real-time how the front is moving through the core and how the fluid changes as the front moves through.” Dennis says that besides all the sophisticated technology available now for monitoring, companies involved in this activity must assure that they effectively reproduce the way that process moves through the reservoir in the rock sample that they have. “It is one thing to flood 130 km2 of reservoir underneath Cantarell and it is another thing to do it in a piece of core that is 50cm or 100cm long. We have to reproduce what we think that rate is going to be during the process and we have to reproduce that same rate flushing through the core.” At the same time, analysts must scale between the reservoir volume and the rock volume in the laboratory, ensure that the pressure and initial welding condition is equal, and that residual oil is at the correct level. Getting the right information on the initial conditions is sometimes also part of the work. “Some of the initial core analysis that we are doing is to actually determine what the initial condition should be when we start the sophisticated EOR process that we want to replicate in the laboratory,” says Dennis. Although complex and time consuming, effective use of sophisticated core analysis can often help an operator understand the best strategy for developing their wells.

“The hydrocarbon system consists of four elements: the structure, which can be evaluated with geophysical methods; a source rock that generates oil and gas, which we can sample and look at in the laboratory; a reservoir with the substance that has to come from the source and get trapped, and it has to have a seal. For the last three elements, it is possible to get actual evidence and analyse it in a laboratory through samples. In the laboratory, we need to look at as much rock as possible, so that we can determine the conditions needed to form a productive hydrocarbon system.”