Figure 1: Shale sample in water- methane gas bubbles

The existence of oil and natural gas in shale formations across the world has long been known by experts in the oil and gas industry.Geologists have understood for decades that shale formations are the source of oil and natural gas from “conventional” production extracted from sand and carbonate rock formations. It has long been known that shale formations contained oil and gas resources (Figure 1). However, the extraction of these energy resources was considered technically impossible to recover because the shale formations lack the permeability (interconnected spaces between the rocks) that would allow the oil or natural gas to flow to a well.

During the 1980’s, activity in the Barnett Shale play of the United States resulted in the development of a successful model for the recovery of natural gas resources from shale formations. The Barnett Shale development model combines two techniques that have been in use for a long time, horizontally drilled wells and fracture stimulation. Fracture stimulation creates tiny pathways within the shale allowing oil and natural gas to flow to the horizontal well-bore.

The combination of these two proven technologies is critical to the successful and economic recovery of oil and natural gas resources from shale formations in the United States, Poland and throughout the world.

How is Shale Gas Recovered?

Horizontal drilling involves drilling a well from the surface downward to a point where the borehole is turned and the well is drilled along a horizontal plane. Figure 3 below illustrates a cross sectional view of a horizontal well showing how the well is drilled downward to a point just above the target formation and then drilled horizontally into the shale. A horizontally drilled well exposes a greater area of the shale reservoir, which allows a greater volume of oil or natural gas to migrate into the wellbore. The greater exposure to the shale reservoir provided by a horizontal wellbore is necessary because of the low permeability of a shale formation. To recover this volume of gas in the past many vertical wells would have been drilled from the surface requiring the use of more surface land.

Fracture stimulation is the second part of the process for the successful recovery of oil or natural gas from shale formations. This process creates small fissures in the shale formation near the wellbore. The process of fracture stimulation has been successfully used in more than a million wells in the United States to date; nearly all natural gas wells drilled today in the United States are hydraulically stimulated, with about 35,000 fracture stimulations happening every year. Fracture stimulation involves the pumping of a fluid, which is primarily water mixed with special additives to carry sand, under pressure to create small fissures within the shale formation. The sand is used to keep these fissures open; these new fissures allow oil or natural gas present in the shale to flow to the wellbore.

Fracture stimulation used in the recovery of shale gas is performed deep underground in multiple stages across the horizontal portion of the well. The number of stages required and the length of the horizontal section of the well are variables researched by scientists and engineers using complex modeling and analytical processes to develop optimal conditions for the recovery of the oil or natural gas. BNK’s test wells that have been drilled to date in Poland show that the target shale formations are located at a depth of approximately 3,500 to 4,500 meters below the surface^[ii].

Figure 4. Water portion of BNK stimulation fluid used in hydraulic stimulation projects in Poland.

Composition of Stimulation Fluids

The composition of stimulation fluids, which is injected into deep shale gas formations that are confined by many thousands of meters of rock layers is mostly water, about 99.9% of the liquid portion of the stimulation fluids used by BNK^[ii] – see Figure 4. The remaining portion of the stimulation fluid is comprised of additives which serve a specific engineered purpose – see Table 1. The additives used by BNK in Poland serve two main purposes; to make the water "slippery" so it pumps more easily and to ensure the water does not get absorbed by the clays within the rock and block the flow of natural gas. All additives currently utilized by BNK in Poland are compliant with REACH, the European Community Regulation on chemicals and their safe use.

Table 1: Hydraulic stimulation additives used in Saponis Lebork S-1 Ordovician stimulation where BNK is Manager and their common uses

How much water is needed and where does it come from?

With water comprising approximately 99.9% of the stimulation fluid, the evaluation and identification of available water sources is an important element of the successful recovery of oil and natural gas shale resources. It is estimated that the average quantity of water required for one stimulation treatment for a single horizontal well is between 11,000 m3 to 19,000 m3^[iii]. Water will come from a variety of sources including groundwater, surface water, brine water and reuse of water from previous fracture stimulation activities.

Protection of groundwater resources

The protection of water resources is a common theme stimulating significant discussion and debate relating to shale gas recovery involving fracture stimulation. Secure well construction is the primary line of protection against pollution of aquifers during the drilling, stimulation and production of shale gas. The process of drilling a shale gas well is no different than the drilling of conventional oil or gas wells that have been drilled in Poland. With more than 7,100 deep wells (wells greater than 1,000 m deep) drilled in Poland, there has not been a reported case of aquifer contamination.^[iv] The development of shale resources in Poland is expected to occur at depths between 3,500 and 4,500 meters. With typical water resource aquifers located at depths of 100 m to 300 m below the surface there are thousands of meters of rock that isolate them from the shale where the gas resource is being produced^[v].

In addition to the protection provided by the thousands of meters of rock, there are multiple layers of steel casings and cement which isolate the inside of the shale gas well from the outer formation and are specifically designed and installed to protect water aquifers. The diagram in Figure 5 demonstrates the layers of protection between the high pressure production casing and groundwater. Additional protection is provided by the pressure monitoring which occurs between the layers of casing – see Figure 5.

[i] Judy Dempsey, “Eastern Europe, Seeking Energy Security, Turns to Shale Gas”, May 11, 2010, nytimes.com, accessed on September 9,2011 at http://www.nytimes.com/2010/05/12/business/global/12shale.html

[ii] BNK, data from a fracturing chemical supplier on a proposed fracturing fluid, received September 6,2011

[iii] Guy Lewis, T. Smith, K.F. Perry, and P. Poprawa, “The Polish Perspective on the Environmental Impact of Unconventional Gas Exploration and Production” in Unconventional Gas – a Chance for Poland and Europe? Analysis and Recommendations, The Kosciuszko Institute, July 2011, 204 pgs.

[iv] Guy Lewis, T. Smith, K.F. Perry, and P. Poprawa, “Environmental Impact of Unconventional Gas Exploration and Production” in Unconventional Gas – a Chance for Poland and Europe? Analysis and Recommendations, The Kosciuszko Institute, July 2011, 204 pgs.

[v] Guy Lewis, T. Smith, K.F. Perry, and P. Poprawa, “Environmental Impact of Unconventional Gas Exploration and Production” in Unconventional Gas – a Chance for Poland and Europe? Analysis and Recommendations, The Kosciuszko Institute, July 2011, 204 pgs.