Sergey Papkov – 3M Oil&Gas Advanced Application Development Engineer
Horizontal wells drilling instead of vertical wells allows to drill directly in the reservoir, wellbore in the productive interval may reach up to 9 kilometers of the horizontal section, thus increasing drainage area several times compared to the vertical wells, drilling in just a few meters in to the payzone.
Enhanced oil recovery methods such as hydraulic fracturing are used to involve in production the largest possible area of productive interval drainage to increase well productivity.
Hydraulic formation fracturing – is the process when fluid directly impacts formation of the rock until it begins to break down and process of fractures creation began. Fracturing is done by pumping a fracturing fluid into the formation (gel, water or acid ) at a pressure exceeding the fracture opening pressure. Depending on the type of reservoir various types of proppants (propping substance) are used in order to maintain fractures in open state, particles used for clastic and sand reservoirs and acid is used for carbonate formations.
Hydraulic fracturing is done to increase oil production, or to increase the injectivity (volume of fluid that injection well can take in) of the injection well. Flow resistance is decreased in the near wellbore zone as a result of fracturing, filtration surface of the wellbore increases.
Proppants play an important role in hydraulic fracturing technology. Proppants – are the solid particles with a size of about one millimeter. Their role is to maintain the newly created crack as a result of fracturing open, after the gel used for the delivery of proppants and create cracks in the reservoir is destroyed. The most commonly used proppants are the grains of sand, sorted up to a certain fraction (particle size distribution).
Application of sand as a proppant in hydraulic fracturing has a number of disadvantages associated with its mechanical properties. Sand is much heavier than water (2.6 g/cm3 for sand and 1 g/cm3 for the water), which means that it will tend to form a slope on its way to reaching the farthest ends of the newly formed hydraulic fracture, this slope that does not allow to use the maximum length of the crack. Another disadvantage of sand is its weak mechanical strength, which leads to its rapid destruction (sand withstand a pressure of about 4000 PSI), which will soon show aup as proppant leaving from the well, and this in turn creates a problem of sand production and loss of geomechanical stability of the reservoir. The solution to both these problems is expensive, forcing oil companies to look for an alternative to traditional sand proppants .
One of the new area of development for 3M are additives for hydraulic fracturing with ultra-lightweight (with a density of 1.05 g/cm3) proppants which density is close to the density of water (1 g/cm3). This property gives ultra lightweight proppants neutral buoyancy, which will hold proppant in solution of water without precipitating . Ultra-lightweight proppants easily reach the farthest ends of the fractures in it and reliably fix there. New generation proppants made deformable and durable (withstands pressure up to 8000 PSI) that will allow them to securely fix the fracture in the open position, without destroying the proppants . Another very important feature of the newly created fracture – is its conductivity (the ability to pass through itself a certain amount of fluid per unit time), the higher the fracture conductivity, the more oil will be extracted from this well.
Speaking of fracture conductivity, it is worth mentioning the way the proppant particles (sand or ultra lightweight proppants) may be packed (create a specific structure) with each other when they are placed in an enclosed pressurized conditions . The most obvious packing structure for particles of sand proppants and ultra lightweight proppants – is a layer. Proppants may be packed as a single layer, and form a multiple layers placed on top of every other layer. Structure consisting of only one layer of proppant is called monolayer. Thus, if a monolayer (one layer of proppant) is not completely filled, ie, to some particles of the layer are missing proppant and instead of proppant there will be a void, then such a structure will be called a partial monolayer (Fig. 1).
It is important to note that only by using ultra lightweight proppants it is possible to achieve partial monolayer structure in the fracture during proppant pumping.
Studies have shown that the conductivity of a partial monolayer of ultra lightweight proppant exceeds conductivity of 5 layers of 20/40 mesh (fractional composition of sand). This fact allows us to establish that with injection of much smaller amounts of ultra lightweight proppants, you can create a fracture with higher conductivity than if sand was used as proppant.
Smaller pumping amounts in the fracture of ultra lightweight proppant to form a partial monolayer structure allow save on the reagents needed for hydraulic fracturing, such as water, polymers, reduce the speed of pumping, saving time for the job. The total amount of savings resulting from the use of ultra lightweight proppants traditionally used instead of sand, in material terms may be 25% of the total fracturing cost.