Investigation on the effect of mud additives on the gelation performance of PAM/PEI system for lost circulation control

Abstract

Lost circulation is one of the most common problems in the drilling of oil and gas wells where mud escapes through natural or induced fractures. Lost circulation can have severe consequences from increasing the operational cost to compromising the stability of wells. Recently, polymeric formulations have been introduced for wellbore strengthening purposes where it can serve as Loss Circulation Materials (LCMs) simultaneously. Polymeric LCMs have the potential to be mixed with drilling fluids during the operation without stopping to avoid non-productive time. In this study, the significance of most common conventional mud additives and their impact on the gelation performance of Polyacrylamide (PAM) / Polyethyleneimine (PEI) has been investigated. Drilling fluid with typical additives has been designed with a weight of 9.6 ppg. Additives including bentonite, barite, CarboxyMethylCellulose (CMC), lignite, caustic soda, desco, and calcium carbonate has been studied individually and combined. Each additive is mixed with the polymeric formulation (PAM 9% PEI 1%) with different ratios, then kept at 130 C for 24 hrs. Rheological performance of the mature gel has been tested using parallel plate geometry, Oscillatory tests have been used to assess the storage Modulus and loss modulus. Moreover, the gelation profile has been tested at 500 psi with a ramped temperature to mimic the reservoir conditions to obtain the gelation time. The gelation time of the polymer-based mud was controllable by the addition of a salt retarder (Ammonium Chloride), where a gelation time of more than 2 hours could be achieved at 130 C. Laboratory observations revealed that bentonite and CMC have the most effect as they both assist in producing stronger gel. While bentonite acts as a strengthening material, CMC increases the crosslinking network. Bentonite has successfully increased the gel strength by 15% providing a storage modulus of up to 1150 Pa without affecting the gelation time. This work helps in better understanding the process of using polymeric formulations in drilling activities. It provides insights to integrate gelling systems that are conventionally used for water shut-off during the drilling operation to replace the conventional loss circulation materials to provide a higher success rate.