Production of CBM. Click to enlarge. Source: GEECL

GEECL uses a hydraulic fracturing process in which a fracturing fluid is first injected into a targeted coal seam. The fluid causes a pressure build-up that propagates the fracture away from the well. Once the fracture has propagated, the operator injects a gelled fluid carrying a proppant (usually sand) to prop the fracture open. Fracture propagation and proppant injection are a continuous process.

After proppant placement, fluids are pumped back. The proppant remains in the fracture, along with some of the entrapped fluids. The operator extracts water to reduce the hydrostatic pressure in the formation so that gas flow can commence.

The CBM readily separates as pressure decreases, allowing it to be piped out of the well separately from the water. Water moving from the coal seam to the well bore encourages gas migration toward the well.

The amount of water produced is high, although it varies from deposit to deposit. The product water must be disposed of; it is not re-injected into the field as in some oil production. The application of the water is determined in part by its composition—the type and amount of total dissolved solids (TDS). But CBM product water generally has a moderately high salinity hazard and often a very high sodium hazard based on standards used for irrigation suitability.

In the US, the Powder River CBM wells have one of the higher water-gas ratios, according to the USGS, at an average 2.75 barrels per thousand cubic feet (MCF) of gas. (Earlier post.)

As of June 2007, GEECL had drilled, perforated and fractured 23 wells and installed the pumps. Nine wells are currently in production, delivering 991 thousand cubic feet (MSCFD) per day, along with 8,030 barrels of product water—a current water-gas ratio of 8.1 barrels of water per MCF of gas. Over time, the water ratio decreases and gas production increases as the beds are dewatered.

With the fourth largest coal reserves in the world, India could be one of the largest producers of CBM. Estimates peg the country’s total CBM resource base at around 16 TCF.

India’s Directorate General of Hydrocarbons (DGH) has approved investing $150 million for drilling 100 production wells in four years.

Reliance Industries (RIL) and Oil and Natural Gas Corporation (ONGC), the country’s two biggest exploration and production companies of conventional oil and gas, have also begun recovering some gas from coal beds. RIL has estimated in-place gas reserves of 3.65 TCF, and ONGC has reserves of around 1.2 TCF.

RIL is likely to start commercial production by the end of 2007; ONGC is planning commercial production in 2008.

Resources:

• 2006-2007 GEECL Results presentation