Abstract
Wettability is usually measured in special core analyses of limited plug samples according to typically costly and time-consuming procedures. For comparative purposes, wettability is considered an index. The two most frequently used wettability indices are the Amott–Harvey wettability index and the U.S. Bureau of Mines (USBM) index. The Amott–Harvey wettability index is linked to imbibition characteristics and the USBM index is associated with the area under capillary pressure curves. To provide a fast analytical method, a mathematical model for predicting the wettability of chalk is presented. The model is calibrated using experimental wettability data and subsequently applied to two wells in Danish chalk oil fields in the North Sea and to outcrop chalk samples. The model supplements traditional labor-intensive laboratory measurements and predicts water wettability variations with depth by modeling both depth and porosity dependencies; in addition, it provides estimates of the effects of the aging time and displacement temperature of chalk wettability measurements in the laboratory.
Highlights
Wettability is defined as the tendency of a fluid to adhere to the surface of a solid material or spread in the presence of other immiscible fluids [1, 2]; it has a critical influence on multiphase flow properties both when one fluid displaces another and when fluids are at equilibrium in a static or flowing system [1, 3]
The objectives of this analytical-experimental study are to investigate the general relationship between the porosity and wettability of chalk samples and to develop a mathematical model for wettability by predicting contact angles under different conditions, such as for different depths, aging times and displacement temperatures
The third trend indicates that water wetness decreases and the contact angle increases with depth and porosity
Summary
Wettability is defined as the tendency of a fluid to adhere to the surface of a solid material or spread in the presence of other immiscible fluids [1, 2]; it has a critical influence on multiphase flow properties both when one fluid displaces another and when fluids are at equilibrium in a static or flowing system [1, 3]. The success of improved oil recovery in chalk fields by water flooding is highly dependent on the wetting conditions of the reservoir rocks [10, 11]. Si and Al in chalk samples originate from calcite, silica and clay, respectively As both the porosity and wetting behavior of chalk are related to calcite, silica and clay content, a link between porosity and wettability is expected and warrants further investigation. The objectives of this analytical-experimental study are to investigate the general relationship between the porosity and wettability of chalk samples and to develop a mathematical model for wettability by predicting contact angles under different conditions, such as for different depths, aging times and displacement temperatures. The model is calibrated using porosity and measured wettability data for samples from deep wells and chalk outcrops
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