Real-Time Wellbore-Drilling Instability in Naturally Fractured Rock Formations with Field Applications

Abstract

Overcoming wellbore drilling instability in fractured-rock formations always presents one of the major challenges to drilling engineers. Due to different fluid-diffusion rates and compressibility degrees between the rock's matrix and fracture network, there are two distinct pore-pressure fields and subsequently different effective stresses developed in a saturated fractured formation. It is recognized that wellbore instabilities such as collapses are caused by excessive effective stress concentrations at or near the borehole wall, and mud losses are due to fracturing the rock formation. Because both the mud/rock fluidpressure differential and fractures' deformation modify the effective stresses in the wellbore wall, such intricate responses require a wellbore solution that accounts for the fracture network, intact rock matrix mechanics, and the balance of drilling mud density. In this work, the effects on real-time collapse and fracture gradients that dictate the safe mud weight window are evaluated analytically, incorporating the effects of natural fracture network via a simulated field case. Analyses reveal that neglecting the naturally fractured nature of the formation falls short in simulating the wellbore instability since it predicted a narrower mud weight window for the drilling operation.

The Effects of Anisotropic Transport Coefficients on Pore Pressure in Shale Formations

“…Formation microscanner images and scanning electron microscopy images revealed that both macroand microscale fractures and fissures within the shale matrix can be recognized [18]. The presence of the discontinuity surfaces (i.e., fractures) in shale for mations has been noted using wellbore imaging techniques.…”

Alkali Solution Erodes Shale: Influencing Factors and Structural Damage Characteristics

“…On the other hand, the bedding planes and natural fractures can propagate due to lost circulation. Lost circulation can cause the decrease of borehole pressure and the damage of wall surrounding rock and then induces the collapse of wellbore [11][12][13][14][15].…”

Nano-fluid loss agent based on an acrylamide based copolymer “grafted” on a modified silica surface

“…Following the invasion of water through the nanopore throats into the shale formation weakens the wellbore and leads to problems such as a stuck pipe and hole collapse. [5][6][7] The solution to this problem is to engineer a nano uid loss agent in the drilling uid to plug the nanopores of shale and shut off the loss of water. As showed in Fig.…”