Abstract

This paper relates severe lost circulation problems often encountered when the well is drilled overbalanced through high-permeability, fractured, or easily fractured formations. As numbers of LCM pills, neat cement plugs were placed in damaging and non-damaging reservoirs, resultant failed to provide an adequate solution.

Recently, severe mud loss problems were encountered during drilling in Mumbai Region from depleted reservoirs, unconsolidated, highly permeable, fractured and fragile limestone formations, both from nonproducing and producing reservoirs (L-III, L-II, L-I, H1A, H3B, etc.). The losses range from 100 BPH to total loss. Attempts are made to stop the losses with the placement of advanced lost circulation treatments. To mitigate these types of losses, an innovative technique developed with a temperature-activated Rapid Setting Fluid (RSF) Pill from indigenously available chemicals and used as an alternative to LCM / cement plugs for severe loss control problems in Mumbai Offshore. The RSF system has proven successful for curing severe dynamic and static losses by pumping treatments through the drill string bottom hole assembly (BHA) (no trip out required) and taking advantage of its highly controllable fast setting properties.

The RSF pill is a stoichiometric mixture of magnesium compound, forming hard and a series of high mol. wt. magnesium inorganic poly-hydrates, displaying characteristics of conventional cement slurry in pumpability, but very different chemically. As the RSF Pill enters the lost zone, it sets rapidly (a rapid transition from liquid to solid) and builds sufficient compressive strength within 5-6 hrs. The reaction causing solidification is wholly a function of time and temperature and unaffected by hydrostatic pressure. The pill is non-damaging as it is non-invasive, sets at the lost zone mouth and 90-100 % soluble in 15 % Hydrochloric acid. The pill can be successfully used up to 140 °C BHST.

The field trial has been carried out successfully in two wells of Mumbai Offshore: N_12#3Z (Mumbai High L-III reservoir) in partial loss conditions and HG#6H (Miocene Bandra Limestone formation) with total losses. It has also established that the new Loss Control Solution, RSF Pill can be placed successfully in all types of lost zones (like L-III, L-II, L-I, H1A, H3B) to mitigate the mud losses.

The paper also details the specific chemical and mechanical characteristics and field performance of the RSF pill. It concludes that the combination of unique fluid properties and best practices in fluid placement procedures plays a vital role in the successful implementation and development in the treatment of loss circulation in limestone formations. This technique is unique, easy, very effective and provides cost benefits.

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