Abstract
Drilling long horizontal sections of directional wells are always challenging due to wellbore stability, hole cleaning, penetration and lubricity challenges. To overcome these troubles, Non-Aqueous Fluids (NAF's) are commonly used and fluid loss control is one of the key essential property that can affect the success of the drilling operation. Globally, conventional powders such as uintaite, grahamite or amine treated lignite are the commonly used fluid loss controlling agents in NAF's due to their ready availability and apparent economic posture. The enhancement in wellbore stability and lubricity as well as reduction in differential sticking, mud losses, and formation damage can be directly influenced effective by fluid-loss control and quality of filter cake properties.
There are two major factors that limit the usage of powders. First, environmental concerns related to fluid's toxicity or biodegradation issues. Industry perception is strong that any asphaltic-based additives are detrimental if discharged into a marine environment. Whilst actual tests to validate this perception may be sparse, more operators are choosing the safe option of apparently costlier solid polymeric filtrate loss reducers. The second key aspect is the potential for formation damage through the solids invasion that occurs during dynamic fluid circulation while drilling before the filter cake is formed. The formation of an impermeable external filter-cake is considered essential for minimizing formation damage, and this should take place as soon as the reservoir rock is penetrated. Once the filter cake is established, the filtration process is controlled by the cake itself rather than by the rock.
The design of a polymeric liquid fluid loss controlling agent is specifically to minimize the formation damage caused by the presence of solids in non-aqueous fluid and to improve the filtration properties with minimal additions when compared to conventional powder treatments. Reduced solids content in the mud helps in minimizing the potential for damage, which consequently has benefits in enhancing the production, by minimizing the solids invasion into the formation. No incompatibility issues were observed with either mineral or synthetic base fluids and the performance of the material was unaffected by temperatures up to 350˚F. The polymeric liquid fluid loss controlling agent functions synergistically with other additives to tighten the fluid loss at significantly lower concentration levels, than would have otherwise been required with traditional asphaltic powders, without negatively influencing the rheological properties of the mud. Another benefit is, No screened out from the mud on shaker screens unlike the powdered material.
This paper reviews the effectiveness of the newly developed polymeric liquid fluid loss controlling agent both in the lab and the field. A case history of successfully drilled wells are discussed with challenges overcome in those fields.
