A New Approach To Estimate Invasion Radius of Water-Based-Drilling-Fluid Filtrate To Evaluate Formation Damage Caused by Overbalanced Drilling

Abstract

Formation damage caused by overbalanced drilling with waterbased mud (WBM) is inevitable as a result of mud filtrate invading the near-wellbore formation. The invasion radius is critical to the multiphase flow when the well is put on production. It contributes to the total skin that hinders the hydrocarbon production. Furthermore, the response of the logging tools may be affected as a result of such invasion, rendering many inaccurate calculations in formation evaluation. To evaluate the skin caused by mud-filtrate invasion, it is important to determine the radius of invasion. A thorough literature review indicated that no practical and reliable method with solid theoretical basis to quantify formation damage is available. Former studies assumed that single-phase drilling fluid displaces reservoir fluid during the invasion. The neglecting of residual reservoir fluid in the invaded zone will introduce error to invasion-radius estimation. This work takes the residual reservoir fluid into account; thus, the estimation of invasion radius is more accurate.This work proposes a practical model to determine the depth of mud-filtrate invasion near the wellbore drilled by WBM. The distribution of mud-filtrate saturation in the near-wellbore region is also calculated by using drilling-operation parameters, mud-filtration-test data, relative permeability, and drilling time. With the accurately determined invasion radius and known wellbore radius, reservoir permeability, and damaged-reservoir permeability, one can evaluate skin factor more accurately. With the knowledge of invasion volume and radius, one can design the wellbore-cleanup procedure appropriately. The proposed model allows engineers to predict the well performance and to diagnose wellbore problems by checking any deviation from the predicted production. This study also can assist with the correction of parameters inferred from log measurements, thereby reducing the over-and/or underestimation of log-derived parameters used in various formationevaluation calculations. Introduction"Skin" is a dimensionless term to be used in diagnosing well performance. A positive skin often indicates the decrease of well performance caused by factors such as formation damage, limited entry, and choked effect. It could also be a negative skin of increasing the well performance, which usually is attributed to well stimulations of acidizing and hydraulic fracturing. For our purposes, the skin of formation damage resulting from overbalanced drilling (OBD) is studied. Hawkins' (1956) equation for damage skin is

Effects of Porosity and Permeability on Invasion Depth During Drilling Mud-filtrate Invading into a Reservoir Dynamically

“…There is not a sharp boundary between invaded zone and uninvaded formation. (b) radial profile of formation resistivity; (c) various invasion depth r i with time t. The invasion depth was the distance from the borehole to the boundary of invasion zone and undisturbed formation [10]. Since the profile of formation resistivity migrated into the deep formation with time, the invasion depth r i varies with the invasion time t as well.…”

Detection of intervals / layers in sections of the wells with anomalous areas of drilling mud filtrate contamination according to the well logging (with negative test results of horizons)

“…Calculations of the size of the invasion zone by solving the direct filtration task [13][14][15][16][17][18] indicate a wide range of approaches to take into account various factors that affect filtration processes in the gradient space around the well. Therefore, considerable attention should be paid to statistical modeling of the invasion zone based on the use of a priori information, which can be obtained from geophysical and other studies in drilled wells [19].…”

Segmented superimposed model of near-bore reservoir pollution skin factor for low porosity and permeability sandstone horizontal gas wells

“…In this paper, when studying the distribution law of pollution radius, various forms of radius distribution of pollution zone are considered (as shown in Figure 7), and the empirical equation and oscillation decreasing function of wellbore pollution radius are combined. Ling et al (2015); Fan et al (2017); Zhang (2017) and others obtained the model of drilling fluid invasion depth in horizontal wells by multiple regression processing of experimental data. Based on the research (Jiang et al, 2023), the distribution law of the radius of the contaminated zone along the vertical direction of the wellbore is given as follows:…”