Formation Damage and Well Productivity Simulation

Abstract

In this paper we describe a simulation model for computing the formation damage imposed on the formation during over-balanced drilling. The main parts modelled are filter cake build-up under both static and dynamic conditions, fluid loss to the formation, transport of solids and polymers inside the formation including effects of pore lining retention and pore throat plugging, and salinity effects on fines stability and clay swelling. The developed model can handle multi-component water-based mud systems at both the core scale (linear model) and the field scale (2D radial model). Among the computed results are fluid-loss versus time, internal damage distribution and productivity calculations for both the entire well and individual sections. The simulation model works in part independent on fluid loss experiments, e.g., we do not use fluid leakoff coefficients, but instead we compute the filter cake buildup and its flow resistance from properties ascribed to the individual components in the mud. Some of these properties can be measured directly, such as particle size distribution of solids, effect of polymers on fluid viscosity and formation permeability and porosity. Other properties, which must be determined by tuning the results of the numerical model against fluid loss experiments, are still assumed to be rather case independent, and once determined they can be used in simulations at altered conditions as well as with different mud formulations. A detailed description of the filter cake model is given in the paper. We present simulations of several static and dynamic fluid loss experiments. The particle transport model is used to simulate a dilute particle injection experiment taken from the literature. Finally, we demonstrate the model's applicability at the field scale and present computational results from an actual well drilled in the North Sea. These results are analysed and it is concluded that the potential impact of the mechanistic modelling approach used is (a) increased understanding of damage mechanisms, (b) improved design of experiments used in the selection process and (c) better predictions at the well scale. This allows for a more efficient and more realistic pre-screening of drilling fluids than traditional core plug testing. Introduction A simulation tool, referred to as Maximize, has been developed for the purpose of investigating fluid loss to the formation during over-balanced drilling and the impairment imposed on the formation by the invading fluid. The objective of the program is to serve as a tool for supporting well planners' decisions related to the choice of well fluids, and integrating, analyzing and interpreting laboratory as well as field formation damage data. The filtration properties of the mudcake forming at the wellbore surface has been investigated by several authors over the years, see for example Ferguson and Klotz (1954); Outmans (1963), Bezemer and Havenaar (1966), Arthur and Peden (1988), Fordham et al. 1991 and Dewan and Chenevert (2001). The common understanding is that once the filter cake has been formed, it will control the filtration rate independent of the formation properties, except at very low permeability where the flow resistance offered by the formation is comparable to the filter cake resistance. The filter cake properties depend only on its composition, the pressure drop over the cake Dp and the shear stress acting on the cake surface by the circulating mud. Under dynamic conditions, the filtration rate will approach asymptotically a limiting steady-state rate which only depends on the shear stress at the cake's surface. A combined filter cake and simulation model was used by Semmelbeck et al. (1995) for computing the fluid invasion profile along the well. Further improvement of the filter cake model was presented by Dewan and Chenevert (2001), who demonstrated the derived model's capability to reproduce complex laboratory experiments with sequential changes in dynamic shear rate and overbalance pressure. Others, have also investigated filtrate invasion by numerical simulations e.g., Ding et al. (2002), Wu et al. (2004) and Suryanarayana et al. (2005).

Mechanisms Involved in Microbially Enhanced Oil Recovery

“…The relative effect of the increased viscous drag introduced by a given amount of deposited bacteria will be larger in high permeability rocks. Simulations of plugging experiments in Lohne et al (2010) indicate that permeability reduction when cells are selectively deposited in the pore throats will occur at a concentration 10 times lower than if the attached cells are uniformly distributed. If the main mechanism for retention is mechanical trapping in the narrow pore throats, rather than attachment by growth on the pore surface, then one would expect increased deposition and higher permeability reduction in low permeability rocks.…”

“…For microbial plugging, the surface area of the attached microbes and of the rock need to be estimated (Lohne et al 2010). The specific surface area (unit: m 2 /ml pore volume) of the rock is given by the Karman-Cozeny equation:…”

Towards Closing the Loop on Drilling Fluid Management Control

“…Following (Lohne et al, 2010) and having sufficient amount of data about drilling fluid composition before and after the circulation, it would be possible to model dynamic effects such as approximate thickness of filter-cake, its permeability and fluid losses to formation. These knowledge will on its hand allow to optimise the distribution of particles when it reaches the bottom of the hole where the filter cake should be created.…”

Surfactant Flooding in Heterogeneous Formations

“…The simulations were performed with an in-house simulator [19]. The simulation models includes two idealized models representing low permeable inclusions embedded in a high permeable background and high permeable inclusions in a low permeable background, and one stochastic model.…”