The primary driver for oil and gas companies is simple – obtaining the greatest volume of product at the least expense. These companies can now economically reach reserves that were impossible to tap just a few years ago. During the last 12 months ADMET has been working with some of the largest corporations in the sector, reviewing their needs and understanding their material testing challenges. This brief paper sets out several of the remarkable innovations being achieved by the sector and how they intersect with the need to test the mechanical properties of the materials involved.
New Innovative Materials and Methods
There have been five big breakthroughs covering numerous technologies which are worth noting:
- Better techniques to find the reserves, such as 3D/4D seismic imaging.
- Fracking, which allows extraction of more material from one well, has been around since the 1940’s but has recently increased in adoption.
- New materials used in the well structure, such as cement and concrete with new additives.
- Horizontal drilling, which has evolved over the last few decades to reach difficult reserves.
- Coil tubing, which speeds the drilling process.
In this discussion we’ll focus on the first three items above and review the role that material testing plays in the success of companies in the sector. Specifically, we will cover some of the methods used to test the unique physical properties of the materials involved in exploration and drilling.
The basic materials such as steel and concrete used in oil and gas drilling have been around for centuries. There is, however, a big difference in the performance of these materials in a typical laboratory environment and their response to the stresses at the bottom of a well, where they are exposed to temperatures and pressures far greater than at the surface. Let’s examine the first big issue, the accuracy of Seismic Imaging.
3D Seismic Imaging for exploration relies on simulated computer models of rock mechanics – the ways in which the rock in the formations will respond to the seismic stimulus. However, a valid model must start with accurate values for the mechanical properties of the materials under in-situ conditions. To measure these values, the downhole conditions must be reproduced as closely as possible in laboratory equipment that tests the material response. How do we reproduce these hostile conditions in the laboratory? We use a specialized device known as a “Triaxial” chamber that allows high pressure and high temperature to be uniformly applied to a rock sample, and then a compressive force can be exerted axially. Material deformations are measured with sensitive strain measuring equipment which allows for the determination of two important mechanical properties known as Young’s Modulus and Poisson’s Ratio. ASTM D7012 – Standard Test Method for Compressive Strength and Elastic Moduli of Intact Rock Core Specimens under Varying States of Stress and Temperatures governs the determination for these properties under confined compression tests. The values established in the laboratory are compared with the field data to further refine the models and provide more accurate predictions of well performance. The next big technology is fracking.
Fracking involves the insertion of a liquid with small particles (sand or ceramic) into a formation under high pressure to expand the rock matrix, the liquid pressure is reduced and the particles remain behind and hold the fractures open to allow extraction of the gas. The compressive strength of these small particles is clearly critical. If they’re not strong enough the fractures will collapse and the well will fail. Mechanical test equipment capable of compressing these particles to the same pressures encountered in the well can verify the strength of the particles and ensure that the maximum potential of the reserve can be tapped. Finally let’s discuss Completion, the final process required before production can commence.
Completion – after a well has been drilled and before it can start production there is a process known as “Completion”. The well is lined with a steel casing to maintain the open borehole and in turn this casing is surrounded by cement. In addition to adding structural stability the cement also seals the edges and prevents gas or liquid from traveling vertically along the outside of the casing, which can cause loss of pressure in the well and even cross contamination across geological boundaries, up to and including groundwater. Certain additives, such as fibers, can significantly improve the structural properties of the cement, but only within certain concentrations – cracking or even collapse can occur if the cement composition is not correct. Testing
ADMET manufactures advanced test equipment used to measure the mechanical properties of materials, including rock, cement, concrete, steel, ceramic, and other materials used in the oil and gas exploration and production process. These systems perform un-confined tension and compression tests according to common ASTM standards such as E8, C39, C109 and C469. In addition, each testing system can be equipped with a triaxial chamber for performing confined compression tests at elevated temperatures according to ASTM D7012. Various cement mixtures becomes a vital part of the pre-production process, and once again the Triaxial chamber comes into play to measure the response of the cement under in-situ conditions.