Core Analysis Essential for Effective EOR StrategiesWed, 01/25/2012 - 10:48
The technique of analysing samples of reservoir rocks in order to learn more about a particular well is almost ubiquitous in the oil and gas industry. Known as core analysis, the process involves taking a cylindrical sample of rock, normally from the side of a drilled oil or gas well. After removing it from the well, the rock is then partitioned into smaller samples known as core plugs, which are typically 2.5cm in diameter and 7.5cm in length. After the extraction of these core plugs, engineers can analyse them to learn more about the geology of the well.
In order to obtain a core sample, operators must halt drilling activities so that the normal drill bit can be replaced with a rotary coring bit, which is similar to a conventional drill bit except for the fact that it has a hollow centre, known as the core barrel. This is designed so that the centre of the barrel remains stationary while the drill bit rotates, and is also designed to store core samples as they are collected. Because drilling must stop for core samples to be taken, the process is relatively expensive and normally only conducted when drilling has to be stopped anyway.
Once engineers have collected the sample, it can be analysed. Core analysis allows geologists to define the porosity and permeability of the rock at different well depths, as well as the level of fluid saturation and grain density, all four of which are key factors in better understanding the conditions of a well and its potential productivity.
The types of cores provided by this type of sampling can range in size from 5cm to 13cm in diameter and approximately 6m to 122m in length. There are four main types of core: full-diameter cores, oriented cores, native state cores and sidewall cores. While oriented cores are taken with a special effort to contain all the fluids of the rock, sidewall coring is usually taken in small bullet-shaped pieces from the sides of the well.
In recent years, there have been advances in the analysis of core samples. One of the companies leading the way in bringing this technology to Mexico is DTK Group, a well services company. John Lawrence, DTK’s Director, explains that the company’s value proposition is based on a mix of specialists that understand both the geology of Mexico and the technology they are using for core analysis. Using this human resource base, the company has successfully introduced sophisticated core analysis to the Mexican market. “Sophisticated core analysis is very important for enhanced oil recovery and increasing or maintaining production in declining fields, which makes it a key technology for Mexico given Pemex’s current strategic priorities,” Lawrence explains.
As well as sophisticated core analysis, DTK is hoping to introduce e-core technology into the Mexican market in the near future. Lawrence explains the advantages that this technology can bring to core analysis: “Currently, measurements are made on cores which are limited to a relatively small section of the well, because it is very rare to get a well that is continuously cored. Generally speaking, when core drilling is conducted at an exploration well, three to five cores will be taken. With five cores, you would have about 45m of information on a 4,500m to 6,000m well, which is not much. But e-core analysis technology enables you to do the same analysis by choosing images taken of drill cuttings, so you can do an angular anywhere on the whole column and then choose the sections from which you want the information.”
Lawrence hopes that one of the biggest future uses of e-core technology will be at Pemex’s planned deepwater projects. “Exploration wells in deepwater will be perfectly suited for the introduction of this new technology to Mexico. As it is a brand new exploration area for Pemex there is currently very little information on the geology, and so it will be very important to gather as much data as possible when drilling exploratory wells. This new technology provides much more data on the geology of wells than existing core analysis techniques. We feel that Pemex will be more open to adopting such a cutting- edge technology where it will have the most impact. Additionally, budgets for deepwater exploration will be larger, which will make adopting the new technology a lot easier for Pemex. We hope that once we have proven the value of the technology to Pemex, they will be willing to adopt it in more exploration areas, including shallow water fields.” Having experience working at Shell’s Perdido development in the Gulf of Mexico, it will only be a small step to build the company’s capabilities in Mexico in order to implement the technology in Pemex’s deepwater fields.