Comparison of Different Type of Acid Diversion in Acid Frac Stimulation and their Effectiveness to Well Production

Acid fracturing has been commonly used to stimulate carbonate formation. Presented in this paper are different types of acid diversion techniques used for one such case. This acid diversion is intended for better acid distribution across long stimulation target intervals. The different types of acid diversion techniques that were used include crosslinked acid, viscoelastic based acid diverter, solid and self degradable fiber acid diverter, and Associative Polymer / RPM based acid diverter. The paper is comparing the effectiveness of the diverter and also the effect of the acid diversion to the well production. The examples that were selected for analysis are producing from the same formation and located relatively close to each other to enable fair comparison. Acid diversion effectiveness is measured based on pressure increase that was observed during the acid fracturing treatment. As the length of stimulation target intervals are different between stages and wells, the pressure increase was then normalized to the length of the perforation / open hole interval. Other than pressure increase, well deliverability post acid stimulation was also compared between wells and was normalized to the reservoir pressure – flowing well head pressure (from available data during well test post acid frac stimulation). These two parameters: normalized pressure increase from acid diversion and normalized maximum gas rate during the well test were then graphed to see the trend between these two parameters. Different types of acid diversion give different pressure increases during acid diversion. In general, the higher the pressure increase, the higher the maximum gas rate. There’s an optimum point of pressure increase from acid diversion that correlates with maximum gas production, which is observed from the wells that were studied. The approach described in this paper is intended to provide the guidance on selecting the type of diverter for acid frac stimulation for better well delivery. This approach is formation specific and the completion type needs to be accounted for when designing similar acid fracturing.