PRACTICAL APPROACHES FOR SOLVING LOST CIRCULATION PROBLEMS WHILE DRILLING
ABSTRACT
As the demand for petroleum resources increases, drilling of oil and gas wells are often carried out in challenging and hostile environments. Among the top ten drilling challenges facing the oil and gas industry today is the problem of lost circulation. Major progress has been made to understand this problem and how to combat it. However, most of the products and guidelines available for combating lost circulation are often biased towards advertisement for a particular service company. The purpose of this study is to develop practical guidelines that are general and not biased towards a particular service company product and which will also serve as a quick reference guide for lost circulation prevention and control at the well-site for drilling personnel.
CHAPTER 1
FORMULATION OF PROBLEM
1.1Â Â Â Â Â Â Â Â INTRODUCTION
Lost circulation is a common drilling problem especially in highly permeable formations, depleted reservoirs, and fractured or cavernous formations. The range of lost circulation problems begin in the shallow, unconsolidated formations and extend into the well-consolidated formations that are fractured by the hydrostatic head imposed by the drilling mud (Moore, 1986). It can then be defined as the reduced or total absence of fluid flow up the formation-casing or casing-tubing annulus when fluid is pumped down the drill pipe or casing. The industry spends millions of dollars every year to combat lost circulation and its associated detrimental effects such as loss of rig time, stuck pipe, blow-outs, and less frequently, the abandonment of expensive wells. Two conditions are both necessary for lost circulation to occur down hole: 1) the pressure in the well bore must exceed the pore pressure and 2) there must be a flow pathway for the losses to occur (Osisanya, 2011). Sub-surface pathways that cause, or lead to, lost circulation can be broadly classified as follows:
- Induced or created fractures (fast tripping or underground blow-outs) Cavernous formations (crevices and channels)
- Unconsolidated or highly permeable formations
- Natural fractures present in the rock formations (including non-sealing faults)
- The rate of losses is indicative of the lost pathways and can also give the treatment method to be used to combat the losses. The severity of lost circulation can be grouped into the following categories (Abbas et al. 2004):
