Modeling Study Unlocks Influence of Capillary Pressure on Sand Production
Chris Carpenter_
This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 36387, “Influence of Capillary Pressure on Sand Production in Unconsolidated Sand Formation: Implications for Capillarity Strength Using Experimental and Mathematical Modeling,” by Mohammed B. Alameen, Ahmed A. Elryes, SPE, and Khaled A. Elraies, SPE, Petronas, et al. The paper has not been peer-reviewed. Copyright 2026 Offshore Technology Conference.
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This study investigates the significant increase in sand production during water injection into unconsolidated sandstone formations. While sand-production rates are primarily governed by changes in rock strength, this research focuses on quantifying the role of capillary pressure (Pc) in modulating capillary strength. By integrating experimental and mathematical modeling approaches, the work aims to advance the understanding of sand-detachment dynamics and formation instability under varying saturation conditions.
Materials and Methods
Sands with particle sizes of 500–600, 300–425, 212–300, 150–212, 63–150, and 63 µm were chosen for this study to represent loose, unconsolidated sand formations. These sands were obtained from a crusher core sample, and the particles were sieved to confirm that all matched the target particle-size distribution (Fig. 1).
A mathematical model was used to determine capillary strength by integrating experimental Pc data with mathematical equations. This model aims to predict formation-strength failure resulting from capillary strength, particularly in unconsolidated (loose-sand) sand formations.
Capillary strength is derived from the capillary forces generated by Pc and interfacial-tension (IFT) force between oil and water at the particle interface. Experimentally measuring these forces and strengths poses significant challenges, making a combination of mathematical approach and experimental study essential. Capillary strength refers to the ability of the initial water to adhere to particle surfaces in porous media. This adhesion must persist when oil is present in the pore spaces, ensuring that any increase in water saturation (Sw) remains confined around the particles rather than flowing through the porous media.
The complete paper provides a detailed discussion of capillary-strength and capillary-force quantification, including related equations.
Mercury-intrusion porosimetry tests were performed, each test consisting of a low-pressure stage (to measure pores with a diameter between 104–105 nm) and a high-pressure stage (to measure pores with a diameter between 101–104 nm).
A Pc curve is required for the reservoir fluids and the reservoir rock. Measurements, however, generally are made with other fluids. A method must be used for correcting the data to provide Pc for reservoir fluids. The corrections are simple and consider the different IFTs and wetting angles for various fluid combinations. The volume of mercury injected into the pores at a given pressure usually is expressed as a proportion of the total pore space. It is presented as a pore-size distribution or converted to oil or gas-brine data using appropriate contact angles and IFTs.