Underbalanced Drilling; Remedy for Formation Damage, Lost Circulation, & Other Related Conventional Drilling Problems

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractAlmost every drilling operation is a potential source of damage to well productivity, lost circulation, differential sticking and other related conventional Drilling problems.This paper re-visits the key damage mechanisims and provides a broad overview on how they occur during various oilfield operations, and their effect on well productivity. Also, lost circulation or fluid invasion potential in high permeability zones, large open fractures, heterogeneous carbonates with massive interconnected vugular porosity, or pressure depleted zones would be a major issue of concern during conventional drilling condition. The worst-case scenario would be a combination of one of these high permeability features with significant pressure depletion.In order to overcome the above problems while drilling, the industry developed a method to drill with a bottom hole pressure below the pore pressure, called Underbalanced Drilling -UBD As the majority of hydrocarbons being exploited today are found in existing pressure depleted or complex and lower quality Reservoirs with lots of the conventional drilling problems, this is where Underbalanced Drilling Technology can add value and in some cases reduce development cost. Soon, Underbalanced Drilling will become the standard field development technique, both Onshore and offshore, where the Geology and Reservoir are suitable.The paper reviews several case histories and real results highlighting the advantages of Underbalanced Drilling Technology in reducing Formation Damage, Lost Circulations and improving well productivity.

Employing a Systematic Scientific Approach to Ensure Successful Implementation of Underbalanced Drilling Technology—Case Study

“…This section presents a detail discussion of key factors that apply to most or all of the individual reservoirs studied. These factors, which significantly impact the UB candidacy score, are: • Solids invasion: This mechanical formation damage mechanism is also known as solids entrainment and is associated with the invasion of solid particulate matter from an external source (Qutob 2004). The two types of external solids that can enter the formation are: artificial solids and naturally generated drill solids or microfines.…”

“…• Formation damage in conventional horizontal wells is often greater than those observed in vertical wells (Qutob 2004). …”

Formation Damage in Tight Gas Reservoirs

“…Advanced Drilling Techniques can assist in reducing the damage potential of the main three damage categories listed below. These will be discussed briefly at the end of this paper [5].…”

Moderate Collapse in a Shale Cap of a Nearly Depleted Reservoir

“…Thus, when using the same drilling fluid density as in the early stage of oilfield development, significant lost circulation and sticking problems will be experienced during the drilling process due to the current lower pore pressure and fracture pressure in depleted reservoirs. Hence, new well designs, such as underbalanced drilling (UBD) technology, were implemented which can reduce formation damage and avoid differential sticking and lost circulation due to lower ECD application [4,14,15]. However, due to the higher collapse pressure in the shale cap above the depleted reservoir, a contradiction existed between maintaining the mechanical stability in the overlaying shale cap and controlling fluid losses in the depleted reservoir caused by hydraulic fracturing [16].…”