Modeling of Drilling Fluid Losses in Naturally Fractured Formations

Abstract

Significant mud losses often occur while drilling in fractured formations. Severe problems arise when drilling fluids invade high permeability conductive fractures that the well path intercepts. The industry has recently started to monitor mud loses in order to identify the fractures and characterize them. Methodologies are available to characterize the geometry and conductivity of the fractures by quantitative analysis of field measurements. These methodologies are mainly based on mathematical models that describe the physical phenomenon and the mechanism under which the flow within the fractures takes place. Once the models are provided one can look for causes of the problem and methods to minimize it.This paper presents a new model for mud loss of non-Newtonian drilling fluids into naturally fractured formations. Flow of Yield-Power-Law (Herschel-Bulkley) fluids has been coupled with Newtonian reservoir fluid in a single fracture. The governing equations are derived based on principles of conservation of mass and linear momentum for drilling fluid and pressure diffusion for reservoir fluid. Results are obtained based on semi-numerical solutions and plotted in terms of mud loss volumes versus time. The results demonstrate how rheology of the drilling fluid and formation fluid properties can influence mud losses. The relative contributions of both drilling and reservoir fluids is determined and compared.This model allows for predicting fluid losses for a given drilling fluid, formation fluid and operational conditions. Conversely, one can evaluate hydraulic aperture of the fractures by continuously monitoring mud losses and finding the best fit of field measurements of mud loss to the model. Field data are used to demonstrate the practical application of the proposed technique.The proposed model is valuable for drilling operations because it can help in minimizing the loss of expensive drilling fluids through optimization of drilling fluid rheological properties and selecting appropriate lost circulation materials. The model also benefits production operations by minimizing formation damage. In addition, well completion schemes can be optimized based on the improved knowledge of the near-wellbore fracture characteristics.

Development of a New Diagnostic Method for Lost Circulation in Directional Wells

“…The other logs that can potentially be used for fracture diagnostics include: image logging, NMR (nuclear magnetic resonance), and microseismic monitoring to obtain information about natural fractures. Unfortunately, image logging and NMR suffer from great practical difficulties to apply during drilling [5,6]; microseismic monitoring does not work well with the narrow single fracture planes encountered during drilling.…”

Study of the performance of LCMs in fractured formations

“…The modifications made in this model account for the fact that the fluid front radius is a function of time, and is given according to Majidi [5], in Eq. (3):…”

Hydrodynamic modeling of mud loss controlled by the coupling of discrete fracture and matrix

“…In addition, the field data on the rheological parameter of drilling mud can be directly employed. Thus, the YPL is subsequently selected as the model to describe the fluid rheology (Majidi et al, 2008a(Majidi et al, , 2008b(Majidi et al, , 2008cPordel Shahri et al, 2011;Pordel Shahri and Mehrabi, 2012;Mehrabi et al, 2012;Livescu, 2012):…”

“…The fracture width can be inversely obtained by fitting type curves and actual data (Lietard et al, 1996). Type curve analysis took the center stage in mud loss studies for a long period of time, and it became the main tool for fracture aperture inversion despite of its low accuracy (Lietard et al, 1996;Verga et al, 2000;Majidi et al, 2008aMajidi et al, , 2008bMajidi et al, , 2008cHoffman and Narr, 2012). Lietard et al (1999Lietard et al ( , 2004 considered non-Newtonian incompressible mud with Bingham rheology to develop a model for the radial mud flow into a non-deformable fracture with constant aperture and infinite length based on Darcy's law.…”

“…However, the facture distribution they used failed to correspond to any practical formation, and the fluid flow between the fracture and the matrix was not considered in their model. Majidi et al (2008aMajidi et al ( , 2008bMajidi et al ( , 2008c proposed a model for simulating the mud loss of non-Newtonian drilling fluids in naturally fractured formations. The flow of yield-power-law (YPL) fluids was coupled with Newtonian reservoir fluid in a single fracture.…”