НУDRAULIC FRACTURING (FRAC) OF OIL FIELD FORMATIONS
METHOD OF HYDRAULIC FRACTURING
Hydraulic fracturing (fraccing - Frac) is the process of creating a large higher conductivity channel in a formation of oilfield to stimulate a longt erm oil flow in tot he well.
DESCRIPTION OF HYDRAULIC FRACTURING PROCESS The special higher viscosity fluid (gel), which is prepared on a water or hydrocarbon liquid (oil, diesel oil) basis is pumped through the oil well tubing at high pressure into a well. The pressure of this fluid breaks the rock of formation over a surfaces of minimum principal rock stresses and as a result of it the fracture appears in a formation. After the fracturing because of continuous fluid pumping, the fracture grows. When the fracture reaches a definite size it is started to enter the special propping agent, called “proppant” (artificial sand with spherical particles made on bauxite basis) intotheliquid. The propping agent is transported by this liquid into the created fracture. The agent keeps the fracture opened after a transportation of liquidis shut off and the overpressure is released. Thus, by the created fracture filled with proppant, the zone of formation drained by well, expands, connects with non explored zones of deposits and a higher conductivity passway is formed to transport anoil into the well. It allows to make an oil yield many times more, to increase the oil recovery rate from a formation and to transfer the part of “out of balance” oil deposits to the production ones.
SPHERES OF APPLICATIONS Hydraulic fracturing (HF) is applied: - for increasing the yield of production wells used in exploration, - for recovering the yield of inactive wells, - as final operation before well completion after drilling in order to get a stable high oil output, - for increasing an injection capacity of injection wells the oil production keeping in situ pressure by drowning .
EFECIENCY OF THE METHOD After fracturing, theratioof oil production increaseis approximately 3. As per the monitoring results, the averaged effect of such treatment lastsnot lessthan1,5 years.
THE PREPARATION JOBS TO FRACCING Usually before the fraccing the geophysical researches are needed to be performed.The researches are conducted with the following purposes: - to investigate an oil displacement within a formation, - to acquire the field exploration data of thef ormation, - to analyze the technical condition of the well, - to investigate the current saturation of the formation, - to investigate thef eature of cement stone bonding with a casing and a rock. Then, based on the results received, the hydraulic fracturing design project is developed, where the specialists the process parameters including the pumping speed and pressure,acontent and amount of an additives pumped ets.
For the HF operation the oil well has to be preliminarily prepared, viz: a well exploration equipment has tobe removed,a special equipment of wellhead connections, flow column and packer (sealed a formation reservoir to bef ractured from a column) has to be installed. All the equipment has to sustain the HF expected pressure with a required coverage factor and to be tested by a proper pressure.
ON-SITE ARRANGEMENT OF HF MOBILE EQUIPMENT COMPLEX
To perform the HF operation the HF special mobile equipment complex is needed to be transported to a well site. The HF mobile complex include : 4-5 pumper trucks ANA-105M, blender truck APS-8M, computer & control center van,manifold truck MM-105M and manifolds unit BM-105, 3-5 technological gel tank cars PTE or BGE,1-2 silos (scid mounted) for PB proppant or proppant carrier (dump-truck oncar chassis). An equipment units of the complex is duly connected one to another and with a wellhead equipment via the manifolds unit as well as by highpressure (HP) and low pressure (LP) pipes. A control systems and gages of equipment are connected via an electrical cables andwires with the computer & control center inorder to monitor the parameters of complex on real time operation mode.
Frac complex is used to hydraulically impact on oil well head zone in order to enhance the yield of non commercial wells.
An equipment automation of high level, data & control station and special software allows to control the frac complex operation via one control console, to monitor simultaneously the parameters of technological process in a real time mode and to automatically submit the results of operation to be conducted.
FRACTURING LIQUID (GEL) PREPARATION
After the HF mobile complex has been localized the fracturing liquid (gel) preparation jobs have to be perfomed. The gels have a high viscosity required to keep the proppant while its delivering into the oil formation. Thegels areprepared on water or hydrocarbon basis. The base of liquid is taken from technological tanks by the blender where required liquid and dry chemicals adds into it and is mixed with themvia the mixer pump and the force pump. Then, a fracturing liquid is pumped back to technological tanks. Thus, the liquid circulates in a closed circuit until it will have had the necessary chemical andphysical properties. A Russia made chemical agents as well as foreign ones are available for a gel preparation. During a gel preparation process, a mobile chemical Lab, located within computer & control center,makesagel sampling and analysis.
HYDRAULIC FRACTURING PROCESS
Prepared Gel goes from technological tanks to the mixing unit where it pass a tandem pumps and is added by a required chemicals. Then, the Gel is delivered to the pumping unitsA A-105Mover HP pipes. The pumping units transport the Gel at high pressure over oil-well tubinginto the well bottom zone of fracture. Injection pressure is defined by the fracture features, is calculated at a design project andcan, if necessary, achieve1050kg/сm2 . During injection of liquid, the fracture arise and expands while the gel is continuously being injecting. After the fracture has been created, from vertical silos the proppant is started to be delivered to the mixer pump of mixing unit. At a mixer pump the proppant is mixed in doses with theGel, coming from tanks. The Gel-Proppant mixture where the proppant concentration may achieve 1800 kg/сm3, is led to the pumping units. They injects it into the formation, filling gradually the fracture by proppant. An amount of proppant, injected to a formation, its density and injection rate are calculatedat development stage of HFdesign project. At a final stage of HF process to achieve a full gel pushing into the fracture the pumping of puregel (without proppant) take splace. After HF process has finished, the packer, a HP flow column are retrieved, a production flow column, pump and production equipment are installed and oil well production starts again.