Operations Hunton Resource Plays

Petroflow has operations in the United States and Canada.

The Hunton dewatering resource play in Oklahoma is the primary focus of Petroflow Energy’s future growth.

Description of Unconventional Hunton Play, Oklahoma

The Oklahoma Properties are part of the unconventional Hunton play.  The Hunton formation is located in central Oklahoma.  Most wells drilled through the formation have indicated oil, either by sheen on the pits, oil stained cuttings, or fluorescence in the cuttings noted by the mud logger.  Many times, based upon these indicators, the formation was tested on the spot.  These tests, called drill stem tests, usually flowed 100% salt water, and the formation was abandoned, or the well drilled deeper to other targets.

Upon subsequent logging of the well, running electrical instruments in the bore hole to determine rock and fluid type, the Hunton would be shown to be "wet", meaning the amount of oil in the formation was less than commercial or even less than what was needed to be productive.  

Even though the Hunton contained oil, it did not produce oil upon test and did not indicate sufficient oil saturation upon logging to be deemed commercial.  The oil observed in these cases is referred to as residual oil.  It is the amount of oil in the rock that is not productive.  Residual oil will not flow under normal circumstances.  Expressed as a percentage of pore space within the rock, the volume of residual oil can be surprisingly high, typically ranging from 30 to 40 percent.  All oil zones have a residual oil component.

Horizontal Drilling of Unconventional Hunton Play

Like the Bakken play in the Williston Basin and the Barnett Shale play in Texas, horizontal drilling has changed the approach to developing the Hunton formation.  Horizontal drilling, drilling a horizontal wellbore within the zone of interest, often for several thousand feet, causes exponentially more of the reservoir to be contacted by the wellbore when compared to a typical vertical well.  This allows for completion techniques which are often impractical with vertical wells.

Horizontal drilling in the Hunton formation allows large scale water withdrawal in a very brief period of time.  This high rate withdrawal changes the fluid dynamics within the reservoir in two ways, both positive.  First, the amount of water in the reservoir relative to oil is quickly reduced.  Consequently, the amount of oil in the reservoir, compared to water, is now increased.  Second, the rapid water removal causes the pressure in the reservoir to drop quickly.  The Hunton residual oil reacts by expanding within the rock pore space due to the high solution gas content of this particular oil.  The combination of high water withdrawal and oil expansion increases the relative concentration of oil to water in the reservoir to a point where it surpasses the residual oil threshold. Oil is now movable within the reservoir and can be produced.  This phenomenon has been observed in new dewatering areas.

With continued high rate water withdrawal and subsequent reservoir pressure drop, solution gas within the oil begins to liberate, and free gas is created within the reservoir.  Free gas expands at a much greater capacity than oil as the reservoir pressure continues to decrease.  Also, as pressure drops, more gas comes out of solution from the oil as free gas.  The process continues to a point where the gas expansion quickly reaches saturation levels where it too is capable of production.  The well begins producing gas in increasing amounts.

During the phase of increasing gas expansion and production, water production actually begins to decline due to the decreasing water saturation in the reservoir relative to gas and oil.  This phenomenon also has been observed in the field.

Gas production will typically increase dramatically, stabilize, then decline over time.  Oil production also increases as gas increases.  As more of the oil converts to gas within the reservoir, the relative oil saturation begins to decrease to a point where it is once again at or below the residual oil threshold.  From this point forward, the remaining oil that is produced is actually condensate from the produced gas.