Neural-net Modeling of Shale-swelling Behavior in Aqueous Drilling Fluids

Abstract

Managing shale swelling is critical when drilling with water-based muds (WBMs). Excessive swelling can lead to shale sloughing, borehole collapse, stuck pipe, and shale disintegration. The fine solids content can increase and cause difficulties controlling rheological properties. Linear swell meter (LSM) testing is a well-known laboratory procedure used to characterize shale swelling in a WBMs.A mathematical modeling tool known as the artificial neural network (ANN) was used to model shale swelling in a WBM. The ANN model establishes complex relationships between a set of inputs and an output based on computational modeling. For ANN modeling of the shale-swelling, the shale mineralogy and fluid composition constituted input parameters, while the output was represented by an experimental characteristic swelling parameter derived from the "% swelling vs. time" data from the LSM test for the respective shale-fluid combinations.Experimental data for building the ANN model was obtained by performing about 250 standard LSM tests on different shales with varying mineralogy and WBMs with varying salt concentrations. This shale swelling ANN model provided excellent correlation with R 2 > 0.9. The ANN model was then successfully validated for an independent set of shale-fluid conditions.Using the shale swelling ANN model, shale-swelling in WBM was predicted for a given shale mineralogy and fluid composition. This reduced the number of trials necessary to determine an optimized WBM formulation. Mud engineers can use this model in real-time as the shale chemistry varies with the depth of the formation drilled. The model provides a helpful measure of fluid performance to determine the optimization necessary to obtain the desired shale behavior. Using this method can help minimize drilling risks and costs associated with unpredictable shales. IntroductionUnderstanding the shale response in the presence of a drilling fluid is crucial to predict and manage borehole instabilities during drilling. Within the drilling industry, researchers have developed several experimental tests and numerical models to describe the interaction between shale and a drilling fluid (specifically, a WBM).Related to experiments, Chenevert and Osisanya (1989) provided various devices that can be used to measure swelling response of shales as they come in contact with WBMs. The effect of potassium chloride (KCl) containing fluids on smectiterich shales was investigated by Horsrud et al. (1998), under both atmospheric and simulated downhole conditions.With respect to computation, Molenaar et al. (1998) described the interaction between the drilling fluid composition and the mechanical behavior of shale based on constitutive models consisting of transport equations for the fluids and the ions. The effect of physio-chemical shale-fluid interaction on shale formation pressure and shale swelling was studied by Huang et al. (1998) using numerical simulations and modeling. In work closely related to this paper, Basma et al. (2003) attempted to implement sequent...

An Experimental Study and Machine Learning Modeling of Shale Swelling in Extended Reach Wells When Exposed to Diverse Water-Based Drilling Fluids

“…Similarly, Kulkarni et al 53 proposed a model to estimate the swelling of shale by including the shale's cation exchange capacity (CEC) and the concentrations of NaCl salt in the drilling fluid. Maghrabi et al 7 constructed an ANN model specifically for forecasting shale swelling in WBDFs. Their model aimed to capture the influence of shale mineralogy and fluid composition on shale swelling.…”

“…The primary objective of extended reach wells is to access remote or hard-to-reach hydrocarbon reserves while minimizing the number of surface locations and drilling costs. , One of the significant challenges associated with extended reach wells is the risk of shale swelling when exposed to different water-based drilling fluids (WBDFs) . Shale swelling occurs when the shale formations encounter WBDFs, leading to the expansion and deformation of the shale rocks. − Shale is composed of clay minerals, which can absorb water and expand. − The interaction between shale and drilling fluids can have far-reaching consequences, including wellbore instability, formation damage, lost circulation, and decreased drilling efficiency. − …”

“…On the other hand, WBDFs commonly known as muds, are widely employed due to their environmentally friendly nature, ease of preparation, and effective inhibition of shale hydration and swelling. − The interaction between these fluids and shale formations can cause shale swelling due to water absorption by the shale rocks. The swelling behavior of shales can vary significantly depending on the mineral composition, organic content, temperature, pressure, and other geological factors. − The risk of shale swelling in extended reach wells is particularly challenging because of the longer wellbore sections and the increased exposure of shale formations to drilling fluids . The complex geomechanical interactions between the drilling fluids and the shale rocks, combined with the extended well trajectory, make accurate prediction and mitigation of shale swelling crucial for successful drilling operations …”

Experimental Investigation into the Effects of Fracturing Fluid-Shale Interaction on Pore Structure and Wettability

“…In addition to organic matter, shale also contains clay minerals, carbonate, and brittle minerals [21]. The clay content in shale is often an important factor affecting shale gas flow capacity, which is due to the swelling of clay when exposed to water [22][23][24][25]. The study of Pedlow and Sharma [23] indicated that the high clay content (over 20%) in shale can reduce the fracture conductivity in 3.5% salty water.…”