Fracturing formation is one way among many other ways to overcome damage and to increase permeability around a wellbore and to increase well sweep efficiency. The fracturing process involves many pieces of frac equipment. Typical frac equipment (Figure 1) installed on a frac site includes a frac pump, a frac blender, a chemical unit, a proppant or sand unit, and frac fluid tanks or frac water tanks. A frac pump provides hydraulic pressure to open fracturing and to deliver frac pad and frac proppant or sand. A frac design will state the required power for example an 895 hp design will be covered by using a 1000 hp frac pump. Frac blender will mix frac fluid, frac chemical, and/or proppant as required before injected into the oil gas well. Some frac design needs 130 bbl/minutes of a frac blender. Chemical unit store additives, proppant unit store proppant, and frac tanks store frac fluid or frac gel. The typical size of the chemical unit, proppant unit, and frac tanks is 200 bbls, 40 ton, and 300 bbls respectively. A control unit or data van is connected to all pieces of equipment through umbilicals. In the control van, an engineer control all equipment, record data, run the frac model, and give input to pieces of frac equipment.
Filtered water or specially designed fluid is required to fracture the formation. The fracturing pressure can be concluded by doing an evaluation of geomechanical stress distribution around the target. Fracturing fluid will fracture the formation in the direction perpendicular to the lowest stress. Generally, the lowest stress is where the fluid coming from. In high water cut well, the well will produce more water after fracturing. Some methods use certain gel to block the fracturing fluid going to high permeability area and losing into the formation. After blocking the high permeability area, the fracturing fluid can be oriented to fracture low permeability area.
Figure 2 shows another method to frac low permeability area. Instead of using certain gel to fracture low permeability area, high permeability area is fractured first to alter stresses around the target, and then before stress alterations dissipated, low permeability area is fractured. Suppose based on a geomechanical stress evaluation, Y direction is concluded the lowest stress with high permeability but the goal is to fracture X direction. The Y direction is fractured first.
Fracturing on Y direction will alter stresses around including low permeability area in the X direction. Fracturing in the X direction is subsequently followed by before stress alterations dissipated as depicted in Figure 3.
An example of the multiple angle fracturing application on the oil field is depicted in Figure 4. Production wells in Figure 4 are overlaid with the facies model map. Production wells located on channel sand have high permeability. Bar sands and shaly sand have relatively low permeability. The oil and gas company has a plan to develop the field to the northwest area of the field. However, to tap the channel sand on X-area, the company will use a multiple angle fracturing method on production well #1. Well#2 and well#6 will follow subsequently. After those sequential fracturing on well#1, the fractured areas will seem like Figure 5.
Multi angled fracturing above is an alternative technique among many other techniques to achieve the fracturing goal. In the April 2009 publication of JPT, several fracturing techniques and operations are discussed.