The impact of weighting materials on carbonate pore system and rock characteristics

The role of overbalance pressure on mud induced alteration of sandstone rock pore system

Overbalance pressure is a very critical parameter in drilling operations. It has a great impact on formation damage, depending on other downhole parameters such as temperature, time, type and composition of mud, and rock mineralogical content. The objective of this study is to determine the degree of the impact of overbalance pressure on mud-rock interaction and the resultant effects on the rock pore system. This research presents an experimental study for the interaction of a Berea Buff sandstone and barite water-based under different overbalance pressure (300, 700, and 1000 psi) under the same temperature and interaction time. The experiments involved the use of the scanning electron microscope and nuclear magnetic resonance relaxation measurements to monitor changes in the pore system of the rock samples. A modified filtration cell was used to accommodate the rock samples and mud at different overbalance pressures. The obtained results showed that the filtration properties, rock flow characteristics (rock permeability, pore throat radius, and pore system scale type) are all affected by increasing the overbalance pressure. The filtration properties increased in terms of mud cake thickness and filtrate volume by 111% and 36% respectively when the overbalance pressure was increased from 300 to 1000 psi. The total rock porosity showed a decrease from 21.6% (pre-mud interaction) to 17.6, 15.2, and 14.2% under 300, 700, and 1000 psi, respectively. The rock permeability decreased by 75% under 1000 psi overbalance pressure while pore throat radius decreased by 45%. However, the rock pore type remains on the same scale (Macro) after interaction with the mud. Statistical analysis showed that the rock porosity and permeability decreased with the overbalance pressure increase through a polynomial relationship with a high determination coefficient of 0.99. Analysis of the internal pore system by the scanning electron microscope showed that the formation damage is mainly attributed to the precipitations of mud solids as overbalance pressure is increased.

Machine Learning Model for Monitoring Rheological Properties of Synthetic Oil-Based Mud

The drilling fluid rheology is a critical parameter during the oil and gas drilling operation to achieve optimum drilling performance without nonproductive time or extra remedial operation cost. The close monitoring for rheological properties will help the drilling fluid crew to take quick actions to maintain the designed profiles for the drilling fluid rheology, especially when it comes to the flat rheology drilling fluid system, which is a new generation for harsh and specific drilling conditions that require flat profiles for the mud rheology regarding the temperature condition changes. The current study introduces a machine learning application toward predicting the rheology of synthetic oil-based mud (flat rheology type) for the full automation system of monitoring the mud rheological properties. Four models are developed, for the first time, to determine the rheological characteristics of flat rheology synthetic oil-based system using artificial neural networks. The developed models are capable of predicting the plastic and apparent viscosities, yield point, and flow behavior index from only the mud density and Marsh funnel as model inputs. The proposed models were trained and optimized from a real field dataset (369 measurements) with further testing the models using an unseen dataset of 153 data points. The predicted rheological properties achieved a high degree of accuracy versus the actual measurements and showed a coefficient of correlation range from 0.91 to 0.97 with an average absolute percentage error of less than 9.66% during the training and testing phases. Besides, machine learning-based correlations are proposed for estimating the rheological properties on the rig site without running the machine learning system for easy field applications.

The Role of Drilled Formation in Filter Cake Properties Utilizing Different Weighting Materials

The filter cake formed during a filtration process plays a vital role in the success of a drilling operation. There are several factors affecting the filter cake build-up such as drilled formation, drilling fluid properties, and well pressure and temperature. The collective impact of these two factors (i.e., formation and the drilling fluid) on the filter cake build-up needs to be fully investigated. In this study, two types of formations represented as limestone and sandstone were used with different weighting materials to assess and compare their impact on the filter cake properties, filtration behavior, and solid invasion. The used weighting materials are manganese tetroxide, ilmenite, barite, and hematite. The filter cake was formed under a temperature of 200 °F and differential pressure of 300 psi. Nuclear magnetic resonance spectroscopy was employed to explore the pore structure of the used core samples. The results showed that the properties (i.e., shape and dimensions) of the different weighting materials are the dominant factors compared to the formation characteristics in most of the investigated filter cake properties. Nevertheless, the formation properties, namely, the permeability and pore structure, have a somehow higher contribution when it comes to the filter cake porosity and thickness. For solid invasion, there were no clear results about the main factor contributing to this issue.