Drill-In Fluids: Identifying Invasion Mechanisms

Abstract

Fluid invasion into productive zones has been widely recognized as detrimental to well productivity. Filtrate and solids invasion can cause irreversible formation damage and permeability reduction. Drilling fluids are formulated to avoid excessive fluid penetration into productive zones. Non-damaging acid-soluble solids are usually added to drill-in fluids in order to promote pore plugging and minimize fluid penetration. Also specific polymers are used that reduce fluid invasion due to surface chemistry and viscosity effects. The development of less invasive non-damaging fluid formulations requires the knowledge of filtration mechanisms of solids containing polymeric solutions in porous media. The work was carried out in two ways: solids with different particle size distributions and concentrations were added to a polymeric base formulation and the filtration behavior of the fluids through unconsolidated porous media was evaluated using computer tomography scanning. Along with the solids investigation, different types of polymeric solutions exhibiting different shear and extensional rheological properties were tested using the same procedure and technique. The extent of the invaded zone could then be measured and the performance of the different types of material could be evaluated. The results from the lab tests will be used to support the development of a filtration model to calculate filtration flow rates and depth of penetration accounting for non-newtonian rheology and type of bridging agent on filtration mechanism. Introduction To better understand the relative importance of factors contributing to filtration, an extensive experimental work is required to support the development of a mathematical model to predict filtration rates and depth of penetration. The paper presents a methodology to evaluate filtration properties of drilling fluids through unconsolidated porous media. Results from static filtration experiments of polymeric fluid formulations are presented aiming: the development of a filtration model to calculate filtration flow rates and depth of penetration accounting for non-newtonian rheology and type of bridging agent on filtration mechanism; the evaluation of filtration characteristics of different fluid formulations; the effect of different polymers and bridging agents on filtration properties of fluids; the development of non-invasive fluid formulations. Background Theoretical and experimental studies on static and dynamic filtration of water based drilling fluids have been carried out to evaluate the effects of fluid type and pH, solids shape, size and concentration, pressure and shear rates on filtration properties of the fluids1. The inadequate control of fluid properties is usually associated with wellbore instability, excessive torque and drag, differential stuck pipe and formation damage2. Therefore, it is imperative to correctly estimate the filtration characteristics of the fluids during drilling and completion so as to properly diagnose and prevent the above-mentioned problems. Moreover, severe fluid losses experienced during drilling in ultra deep waters have brought the attention to the need for non-invasive fluids to guarantee a successful operation. One of the main problems related to the presence of filtrate in productive oil and gas zones is the significant permeability reduction and well productivity decrease. The modeling of filtration process as to predict permeability changes and depth of damage penetration into the productive zone is essential to establish the stimulation technique that will better remove the existing damage3.

Drilling muds with stable rheological parameters using modified natural polymers

“…The improvement of gel strength and the possibility of reducing the concentration of natural polymer in the drilling mud (cost reduction) can be obtained by applying modifications with the use of appropriate metal ions. The possibility of reducing the polymer concentration in the drilling mud in this case is a result of significant increase in viscosity due to the molecular weight increase (Kramer et al, 1987;Harris, 1993;Himes et al, 1994;Queiroz and Santos, 2000;Lomba, 2002;Suresh Kumar et al, 2012;Dupas et al, 2013;Luyster et al, 2016;Zhu et al, 2017).…”

Evaluation of PAC with Nanoclay as drilling mud

“…Invasion of fluids to productive regions can exert negative effects on well productivity. Since the invasion of filtrate and particles can result in irreversible formation damage and decreased permeability, the mud cake needs to be formed as fast as possible to prevent the damage caused by solid particles and cuttings [1]…”

Effective Bridging Agent Particle Sizes of Reservoir Drilling Mud

“…Bridging agent is a material that is formation-dependent, thus suitable to be added to the drilling fluid of drilling operations in unconsolidated formation and the particle size selection of the bridging agent need to be optimized.In another way, bridging materials are also drilling fluid additives that act together with fluid loss control products to minimize fluid invasion into the formation. The correct choice of bridging material type and concentration is crucial to create a low permeability filter cake and minimize formation damage (Lomba et al, 2002).…”