University of Durham
Crude oil and natural gas, occurring in permeable, buried rock strata known as reservoirs, are described as “conventional hydrocarbon” resources. Impervious rock seals, called cap-rocks, keep buoyant oil and gas underground in the reservoir. Owing to the way the reservoir formed, the cap-rock is usually a shale, consisting of a large amount of compacted, microscopic, plate-like clay minerals.
The properties of clay minerals will be familiar to those living where the soil has high clay content. During dry periods clay soils dry out and shrink, with large cracks appearing in the ground. Conversely, during wet periods, the clay hydrates, expands in volume and loses it cohesiveness, forming a viscous mud.
The clay behaves in this way due to its structure at a chemical level, with the clay crystals made up of many layers, each only a nanometer (millionth of a millimeter) or so thick. Water is attracted to regions between the layers, making the clay expand and, eventually, fall apart.
The same happens when an oil company drills an oil or gas well through the clay rich shale cap-rock. Water, from seawater, or the fluid used to remove the cut rock, will enter the shale formation and make the clay minerals swell, leading to well-bore collapse and the drilling operation may need to be abandoned, costing many millions of dollars.
It is critical for the drilling company to be able to know if a particular shale formation may become unstable and what can be done to prevent this occurring during the drilling of the well bore. A key challenge, studied in this Fellowship at Durham University and M-I SWACO, is to use information from related shale rock systems present at the Earths surface (outcrops) and artificial shale, made in the laboratory from representative minerals, to be able to predict and understand hydration of shale below the surface, during drilling operations. The same research is relevant for enhanced oil recovery and developing novel materials.
Interests and expertise (Subject groups)