When Magnifying Your Reservoir Shows More than Expected Details: How Logging-While-Drilling Electrical Images were Used to Perfect Drilling Practices and Minimize Borehole Impact

Abstract

Ultrahigh-resolution electrical images (UHRIs) acquired with logging while drilling (LWD) tools have brought to light different side effects of using drilling tools such as rotary steerable systems (RSSs) and bits when drilling a horizontal borehole. This paper will go through the extensive analysis and simulations that followed, gathering data from almost thirty wells, to try and understand the root causes behind these side effects, along with the actions put in place to mitigate it. UHRIs were used while drilling a 6-in horizontal hole to achieve a 100% net-to-gross and perform advanced formation evaluation to optimize well production. Surprisingly, these images revealed more details: wellbore threading–a type of spiral–inside the formation. To understand the cause behind such marks, RSS and bit data was gathered from around thirty wells, compared, and analyzed. Simulations were run over months, considering rock types, drilling parameters, and bottom hole assembly (BHA) design to reproduce the issue and propose the best solution to prevent these events from reoccurring. After the data compilation, a trend emerged. Wellbore threading was observed in soft, high-porosity reservoir formations. It also appeared in tandem with controlled rate of penetration (ROP), low weight on bit (WOB), and a low steering ratio. At this point, advanced analysis and simulations were needed to determine the root cause of this phenomenon. A Finite Element Analysis (FEA) based 4D modeling software showed that the bit gauge pad length, combined with the RSS pad force, contributed to this threading. A pad pressure force higher than 7,000 N in conjunction with a short-gauge bit increased the likelihood of having this borehole deformation. Simulations comparing different size tapered and nominal bit gauge pad lengths were run to determine the effect on the borehole and on the steerability. Bit design is directly linked to the wellbore threading effect. It is more pronounced when associated with a powerful rotary steerable system and in a soft formation environment. However, altering a specific bit design can have a direct and undesirable effect on the steerability of the BHA. UHRI revealed details of borehole deformation that new drilling technologies are causing. It enabled an in-depth analysis of the different causes behind it, revealing ad-hoc solutions. Horizontal wells are being drilled in more challenging environments such as through thin formation layers, unpredictable geology, and unknown fluid movement. Detailed evaluation has a direct impact on the completion approach. But we also need to drill faster and more efficiently. The wellbore threading caused formation damage that masked information needed for formation evaluation. In a novel application of UHRI data, simulations gave birth to information which has been lacking and incentivized the development of new, formation-friendly technology.