Influence of Oil Flow on Water Content

Abstract

Experiments performed with distilled water, unconsolidated sand and dead oilfor the purpose of determining the influence of oil flow on the water contentof sands were described. While results found are not necessarily, therefore, identical with those that would be obtained under natural petroleum reservoirconditions, the following conclusions were drawn.When oil under constant head is flowed through an unconsolidated sand, theamount of water retained in the core is inversely proportional to the specificpermeability of the core. This corroborates the view that the degree to whichoil displaces.water out of the pore space is limited by the size of thepores.For the range investigated, the displacing action of a more viscous oil ofhigher specific gravity was found to be the same as a less viscous oil, orlower specific gravity.The amount of interstitial water retained in the sand bears an inverserelationship to the pressure head of the displacing liquid.The degree of retained water saturation of the sand appears to approach 100per cent as the specific permeability approaches zero.For the higher values of specific permeability and for the pressure rangeinvestigated the remaining amount of water in the sand occupies approximately10 per cent of the pore space. This, together with the fact that the limitingoil velocity curve approaches approximately 10 per cent water saturation as anasymptote, indicates that beyond this point removal of water is achieved onlyby a stripping of the grains requiring considerable pressure drops across thesands; or by a balancing of the molecular forces.As the water saturation of the sand exceeds approximately 15 per cent of thepore volume, the permeability of the sand to oil decreases rapidly.Sands with water saturations as high as 40 per cent were found to produce100 per cent oil.

Field Application of Core Analysis and Depth-pressure Methods to the Determination of Mean Effective Sand Permeability

“…For these conditions it can be shown that [3] in which "/0 = density of fluid, g = acceleration of gravity, C = well characteristic as shown by Eq. 2, t = time after shut in, in seconds, A = effective cross-sectional area of the well bore, P, = reservoir pressure, P, = initial steady-state flowing pressure, P = pressure at any instant t. rw If for any particular set of well data a plot of Eq.…”

“…3 depth-pressure measurements. Permeabilities determined from actual reservoir data inherently reflect the obstructional effect of the connate water, so that the results of such an analysis will give directly the mean effective permeability.…”