Hydraulic fracturing of benches

Hydraulic fracturing of benches - one of the most effective levers on a face band of slits. It is a method it is applied to assimilation of slits for raise of efficiency oil and gas fields and for raise of adsorptive capacity of injection holes, at isolation of local waters etc.

Process of a fluid fracturing of benches consists in making artificial and expansions of available slits in soils of a face band action of positive pressure of the fluid forced in a slit. At pressure increase in seam soils are formed new or available rends are opened or dilated. All this system of rends links a slit to the productive parts of a seam eliminated from a drift. For prevention of closing of fractures after release of pressure in them enter the coarse-grained sand added in a fluid forced in slit. The radius of rends can reach several tens metres. Hydrodynamic efficiency of a method and the max magnification of rate of flow as a result of a fluid fracturing of benches can be valued, proceeding from the following.

Fractures, in comparison with a porous medium of oil manifolds, possess higher track capacity, therefore it is possible to suppose, that fluid conductivity of well in radius of a rend after a disrupture became perpetually major. Then run to such slit it is possible to calculate, taking over its radius equal to rend radius. Hence, at the same depression where Q (t) - rate of flow with radius r (t); the Q-PRODUCTION RATE of a perfect slit with radius r (c); R (k)-radius of an outline of a food.

(lg ((R (k)) / (Q (t))) / (lg (q / (r (t)))) = (r (c)) / (R (k))

Trade practice demonstrates, that debits slits after a fluid fracturing are incremented sometimes in some tens times. It testifies that the formed rends, apparently, are bridged with existing earlier, and well stream happens also from earlier quarantined highly productive bands.

The cracking gear at a formation fracturing a fluid filtrated in a seam following. Under pressure, created in a slit pump units, breakdown agent is filtrated first of all in bands with the greatest penetrability. Thus between brats on a vertical there is a pressure difference, as in more permeable brats, pressure more than in poorly permeable or practically not the permeable. As a result on roofing and a trough permeable a seam some forces start to act, above superjacent soils are exposed to deformation and on boundaries of brats cross joints are formed.

At a disrupture not filtrated fluid the formation fracturing gear becomes similar to the gear of a disrupture of heavy-wall receptacles. Rends formed thus have, as a rule, a vertical or raking direction. At a disrupture a filtrated fluid the bursting pressure is routinely significant less, than at a disrupture not filtrated fluids, as in the latter case the gear of a disrupture of soils of gangway boards with the gear of a disrupture of a heavy-wall receptacle. The filtrated fluid which has nestled in a seam in a consequence of a major contacting area with soil, Transmits to it major efforts, sufficient for a disrupture at pressures, is significant smaller, than it is necessary for breaking down of a seam by a not filtrated fluid.

Disrupture process in a major degree depends on physical properties of a fluid and, in particular from its viscosity. That the bursting pressure was the least, it is necessary, that it was filtrated.

Viscosity raise the same as also reduction of filterability of the fluids applied at a disrupture of benches, is realised by injection in them of the applicable additives. Such stiffeners for the hydrocarbon fluids applied at a disrupture of benches, are salts of organic acids, high-molecular and colloidal jointings of naphthas (for example, oil tar oil and other waste metal of oil refining).

The significant viscosity and high sand a bearing strength some naphthas, kerosene - lead-acid and naphtha - the lead-acid emulsions applied at a disrupture of carbonate manifolds, and water - oil emulsions possess. These fluids also are used as breakdown agents and fluids - of sand-carriers at a disrupture of benches in oil-wells.

Application of breakdown agents and fluids - of sand-carriers on a hydrocarbon bottom for a disrupture of benches in water injection holes can lead to impairment of permeability of strata for water owing to formation of mixtures of water with hydrocarbons. In order to avoid this phenomenon seams in water injection holes rupture thickened water. To gelling apply sulphide - the alcoholic grain stillage and other cellulose derivatives, well water soluble.

The sand intended for infill of rends, should meet following requirements:

1. To form strong sandy solepieces and not to be wrecked under pressure
2. To store high penetrability under the influence of external pressure

To these requirements contents coarse-grained and uniform sand on the grain composition, possessing high mechanical strength. The greatest application was received by pure quartzy sands with aggregate size from 0,5 to 1,0 mms.

Technology of carrying out of a fluid fracturing of a seam

For a seam fluid fracturing first of all choose slits with the low efficiency, caused by natural small permeability of strata, or slits, filtration capacity of which one face band was degraded at formation exposing. It is necessary also that the formation pressure was sufficient for providing of run of naphtha in a slit. To a disrupture of soils a slit probe on run and spot its adsorptive capacity and pressure of absorption. Effects of flow test and data about adsorptive capacity of a slit before and after a disrupture give the chance to judge effects of operation, help to value roughly a bursting pressure, correctly to select eligible properties and quantity of a fluid for disrupture carrying out. To judge variations of permeability of strata of a face band after a disrupture. Before the beginning of operations a slit clean of a mud underground draining and flush to refine filtration characteristics of a face band. Good effects of a disrupture can be received at pretreatment of a slit saline or mud acid (a mixture saline and fluoric) as at formation exposing permeability of strata is degraded in those intervals, much more all the filtrate and a mud make through. Such brats are most permeable leases of a section which one after formation exposing at drilling on a mud become sometimes a little permeable for breakdown agent. After prestress acid treatment filtration characteristics of such benches are refined and there are the favorable conditions for cracking.

In the flushed cleaned slit drain off pumping tubes in diameter of 76 or 102 mms on which one breakdown agent impinges on a drift. At draining off of tubes of smaller diameter owing to the significant pressure losses disrupture process is impeded. For safeguarding of a casing from action high-pressure over a seam the packer is erected. That it did not move on a string at positive pressure on tubes it is recommended to erect a hydraulic armature. The more pressure in tubes and in an armature, the with great force ring-type facets at butt pistons being indented in колону are advanced and nestle pistons armatures on a casing, render those major braking effect, than above pressure. Are available an armature and other types.

The well head is arranged with a special horsehead to which one hook up aggregates for pumping of fluids.

The formation fracturing is realised by pumping in tubes of breakdown agent till the moment of lamination of a seam which one is marked by substantial growth of coefficient of injection capacity. After a disrupture in a seam force a fluid - a sand-carrier. The greatest effect is yielded by injection of a fluid of a sand-carrier at major velocities and pumping HPs as the formed rends thus are more widely opened. A fluid - a sand-carrier press through in a seam in bulk of tubes by pumping in a chaser slit in which one quality use naphtha - for oil-wells and water - for blowing. After that a well head cover and leave her alone until pressure on a mouth will not wane. Then a slit flush, clean of sand and initiate with its assimilation.

Except the featured plan of a fluid fracturing, depending on conditions of carrying out of process and its assignment apply other flow diagrammes.

In ebb slits the formation fracturing can be conducted without draining off pump - compressor tubes or with tubes but without a packer. In case of the former the fluid is forced immediately on case pipes, and in second both on tubes, and on hole annulus. At such technology it is possible to moderate considerably pressure losses in a slit at pumping very much viscous liquid. It is possible to apply to meliorating of conditions of run and a repeated formation fracturing. Its essence consists that in a seam on miscellaneous depths some rends and thus create, essentially increment permeability of strata of a face band in slits

Rather relevant question at the carrying out of a fluid fracturing demanding special attention, also is the position determination and character of formed rends. This task is successfully solved by methods of the radiation logging conducted after injection in a rend of a mixture of usual and radioactive sand. Sand activation realise adsorption and binding on its surface of radioactive substances. The adsorbed active ingredient can be anchored by cover of grains of sand water-insoluble and naphthas gluing matters. On curves a gamma - of a core drilling in the range of cracking there are accurate anomalies of radioactivity