Alteration of Saudi reservoir rocks wettability due to drilling fluids contamination

Abstract

Wettability is a key parameter that affects the petrophysical properties of reservoir rocks. Mud filtrate during the drilling of the pay zone causes a significant change in rock wettability that will affect the oil production and enhanced oil recovery methods [EOR]. This change depends on the mud filtrate and the oil rock systems involved. The objective of this paper is to investigate the influence of water base mud, oil base mud, and Partially Hydroxide Polyacrylamide (PHPA) mud filtrate on the reservoir rocks wettability. The drilling fluid formulations that recommended for drilling horizontal wells had been used in this study. The reservoir rocks used were Saudi water-wet sandstone and limestone. The contact angle was used to measure the rock wettability. Also, the effect of temperature on wettability alteration had been studied. The results showed that the rock samples used are originally water-wet. Water-based drilling fluids tend to make the system water-wet. The contact angle tends to increase with increasing NaOH and KOH additives at both 25° and 60°C. In contrast, oil-based drilling fluids change the system from water-wet to strongly oil-wet. This change is higher with crude oil than with diesel oil. PHPA mud contamination strengthen the wettability of water-wet reservoir rocks towards water. The effect of temperature increase is variable. It increases the contact angle with oil-based mud while reduces it with water-based and PAPA muds. This change is higher with limestone rock than with sandstone rock.