دانلود رایگان ترجمه مقاله مرور افت مواد گردشی و آمایش ها با طبقه بندی به روز

مرور افت مواد گردشی و آمایش ها با طبقه بندی به روز

Review of Lost Circulation Materials and Treatments with an Updated Classification

Abstract

Drilling fluid losses are considered one of the major contributors to drilling non-productive time (NPT). Lost circulation materials (LCM’s) have been widely used to avoid or stop losses. Due to the large number of current available LCM’s and their different applications, classification and testing of LCM’s is very important. Conventional LCM’s are currently classified into different categories based on their appearance as fibrous, flaky, and granular or a blend of all three. The most recent LCM classification was published around 50 years ago and this paper intends to fill this gap with an updated classification including conventional and new technologies. We propose to re-classify LCM’s into 7 categories based on their appearance and application as: granular, flaky, fibrous, LCM’s mixture, acid/water soluble, high fluid loss squeeze, swellable/hydratable combinations, and nanoparticles.Particle plugging apparatus (PPA) and HPHT fluid loss apparatus in conjunction with slotted/tapered discs are used to evaluate LCM performance for corrective treatments. Until now, no single standardized testing method or interpretation that evaluates LCM’s performance when preventive treatments are applied in order to increase the fracture gradient has been developed. The difficulty in standardizing the testing methods is due to the disagreement about wellbore strengthening mechanism. This paper discusses the most recent developments in lost circulation materials such as plugging assurance technology and nano-technology, in addition to the presentation of a comprehensive summary of today’s available LCM’s.

1 Introduction

With the significant increase in oil demand, a huge number of conventional hydrocarbon resources are being depleted. As a result, more challenging drilling operations are required. When drilling challenging wells, such as extended reach wells or deep water wells, the operational mud weight window narrows. The lower limit is increased due to higher collapse pressure in deviated well while the upper limit, controlled by the fracturing gradient, is reduced due to higher equivalent circulation density (ECD) in extended reach wells, damaged wellbores, and lower overburden gradient or as a result of wellbore deviation. This decrease in the operational mud window can lead to common problems such as lost circulation. Lost circulation incidents could lead to a series of unwanted consequences that could cost up to million dollars or more 1 . The severity of the consequences varies depending on the loss severity; it could start as just losing the drilling fluid and it could continue to a blowout. In general, lost circulation events are classified based on the losses rate (bbl/hr.). When the fluid loss rate is 1-10 bbls/hr., the loss is classified as seepage loss which could happen in any type of formation. As the fluid loss rate increase from 10 to 500 bbls/hr., the losses are recognized as partial losses that could occur in gravels, small natural horizontal fractures, or induced vertical fractures. Once the loss rate increase to 500 bbls/hr. and above, the losses are considered to be complete losses 2 . Lost circulation events may occur in naturally fractured formations, cavernous formations, highly permeable formations or due to drilling induced fractures (Fig.1).One of the early efforts to cure losses or prevent them from happening by adding granular materials to the drilling fluid, was introduced by M T. Chapman in 1890 3 . Since then, lost circulation materials have been widely used to stop or mitigate drilling fluid losses into the formation. LCM’s are added continuously to the drilling fluid system or spotted as a concentrated LCM’s pill in order to seal naturally existing fractures or induced fractures that are produced while drilling.

Lost Circulation Treatment: Corrective vs. Preventative

The way that lost circulation treatments are applied could be classified based on the time when these treatments were implemented. It can be either before (preventive) or after (corrective) the occurrence of the lost circulation event:

Corrective Methods

This approach treatment can be defined as any method that is applied after the occurrence of the losses 1 . In this approach, lost circulation treatments are either added continuously to the drilling fluid or spotted as a concentrated pill in order to mitigate the losses. There is a wide range of corrective lost circulation treatments depending on the type of losses or the type formation being treated. For seepage and partial losses, LCM blends are added to the mud in various concentrations. The addition of LCM’s into the mud will help reducing seepage and partial loss, but when severe losses are encountered; other treatments are required to solve the problems. For severe losses, settable pills such as cement plugs, gunk, deformable or soft plugs are often used to gain circulation. Deformable, viscous and cohesive plugs (DVC) are claimed to be effective due to their physical properties such as the cohesion which helps in creating an impermeable seal thus preventing the drilling fluids from leaking into the fractures 4 . These types of treatments require special placement and mixing procedures that need to be taken into consideration. For depleted or highly permeable formations, high fluid-loss high solid-content squeeze pills are used to mitigate the losses when encountered 4 .