Single-Phase Flow Through Natural Fractures

Abstract

OOPY%@t lW. sOOiOfY of Petroleum Engineers l%&I&MI&ww&w~5~&aonta!bn at tfre 6Srd Annual Tachnkel CeMarenca and Ex5ibltkm of tha SocIaty of Patroleum Englnaara hold in e, -,. LasmAczIt is well known that for q single-phasefluid flowing beteeen smooth parsllelplates, the pressure drop is proportional to the cube of the aperture septrathg the plates. Some .investig8tors2 vS have looked qt the qffect of surface rougbmesson flow ueing fabricatedsurfaces, inducedfractures, or sawed $urfaces and have found deviation from that law at small aperturee. This paper preeenttr new laboratory data for single-phaseflow throughopen roughnatural fractures.Tvo typea of petroleumresenroirrocks (sandstones and cherts ) were used, each having a differentsurfs.ce rougbness. Flow through both open snd closed fractures is evaluated with apertures ranging between 0.002 to 0.0253 in. A techniquefor maasuringapertures in-situ has been developedwhich avoids backcalculatingaperturesfrom flow data, as other investigatorshave had to do. Fluids with viscositiesof about 1 and 18 cp were used.At large apertures (0.0253 in), compared to the surface roughness, the cubic law ie followed; at smaller aperturee for rough fracturee,deviation is seen. Transitionfrom leminar to turbulentflow is smooth but is dependent on surface roughnese for 9mallerfractureqperturbs. CriticalReynoldsNumber, the ReynoldsNumber where leminar flow enda, ia seen to decrease with decreasing fracture aperture for rough fracturee. Data are correlatedusing plots of frictionfactorversusReynoldsNumber.Many reservoirs are fractured to some degree. These natural fracturesmay have substantial or little contribution to the overallflow characteristics of a --Referencesand iHuetrationsat end of paper. reeervoir, depending on the differencebetween the matrix and fracturepermeabilities end the number of fractures. In reservoirshaving good matrix porosity and permeability,productioncontributedby fractures may be so insignificant that fractureein the~~trix qre undetected. In other fracturedrese=o<rs which have 10V matrix permeability, fracturepermeabilitiee may contribute most of the fluid flow and control fluid production.A reservoirfracturesystemis a cofeplex matrix of inter-connecting and non-connecting fractures. A completeunderstanding of singleand multi-phaseflow is currentlyprecludedby the lack of experimentally derived equatione for flow in fracturedchannels or acroas a fracture/matrixinterface. Before these multiple fracture casee can be considered, flow througha singlefracturemuet firstbe understood. Flov in a fracture is normally characterized by using the claesicalcubic law equation(Witherspoonet all) for steady-state isothermal, laminarflow between two parallelplates: [1 vhere Q -flow rate (bbl/day) V = width of fractureface (ft) AP -pressuredifferential (psi) b -fractureaperture(in) L = lengthof fracture(ft) P = fluidviscosity(Cp) Ae noted, this equationassumesthat the walls of a fracture are smooth parallalplates; the walls of naturalrock fractureeare not. Work in the 1940'e b...

The influence of surface roughness on fluid flow through cracks

“…This finding was in general accord with that reported in Ref. [2] and will be returned to subsequently.…”

“…Jones et al. 2 looks at laminar flow through rough natural fractures as occur in rock. Here a dependence of friction factor on roughness is observed and with λ ‐values of some 100 recorded.…”

Flow and Transport in Fractured Rocks

“… Evans and Evans [1988] showed that the presence of immobile or low mobile liquid saturation in a simulated hydraulic fracture could enhance the nonlinear flow. For liquid flows, especially in fractures near wellbores, the nonlinear effects could be significant [ Guppy , 1987; Morris et al , 1987; Jones et al , 1988; Jung , 1989].…”

Identifying Wellbore Damage Components through Discrete Fracture Network (DFN) Models

“…In naturally fractured reservoirs, the fluid enters to the well through the discrete open fractures intersected by the wellbore. Fluid flow through individual (discrete) fractures has been studied experimentally by Jones et al 2 whose conclusions were that the roughness of fractures play an important role causing turbulence and additional pressure drop. The smaller the fracture apertures the higher the roughness influence on turbulence effects.…”