A Case History of Reservoir Subsidence and Wellbore Damage Management in the South Belridge Diatomite Field

Abstract

Thw paper was prepared for presentatmn al tfw Western Regional Meeting held m Anchorage, Alaska, 22-24 May 199S This paper was selec!ed lor presentahon by the SPE Prcgram Comm!tlee folfowmg revmw' of Informalton cnntamed In an abstracf submmed by the author(s) Contenls of the paper as presented, nave nO[ been rewewed by the Soctety of Petroleum Engnwers and are subjecf to correcton by the authcr(s) The maternal, as presented, does not necassanly reflecf any POSIIIO"of the Society of Petroleum Engtneers or idsm-mbersPapers presented a[ SPE meetlcgs are subject 10 publlcatum rewew by Edional Comm!ttee of the SomBly of Petroleum Engineers Permwsmn to COPY!s restricted to an abstract of not more than 3C0 works Illustrations may not be coped The abstract should contain conspicuous acknowledQmam of where and by whom the IXILI.X was presemed WWo L\brarvan, SPE, P O 833836 Rlchardso", TX 75083-3836 USA, fax 01 -214-952:!+435 ABSTRACT Production of fluids from the shallow, thick, and low-strength Diatomite reservoir in the South Belridge field has resulted in reservoir compaction, surface subsidence, and numerous well failures. The most severe subsidence problems occurred while the field was under primary recovery, prior to implementation of waterfloods for pressure support, Consequently, a significant number of wells in the field have incurred casing damage, which proportionate y limits the utility of these wellbores for cent inued production and routine wellwork operations. The nature of casing damage varies significantly depending on the location in the field, however casing shear ("kinks") generally produces the most severe problems in retaining full wellbore utility since it Iim its tool passage (e.g., packers, scrapers, etc.) and is not economically repairable using conventional milling tools. Since the mid 1980s, surveillance activities have been in place to monitor and assess the magnitude and progression of surface subsidence, reservoir compaction, and wellbore damage in Section 19 of the South Beh-idge field. Surveillance activities include the use of ground elevation markers and a variety of production logs --several of which involve novel application and log interpretation. These data subsequently were used to develop and verify hybrid geomechanics and wellbore geometric models for assessing casing damage, identifying well operability and wellbore utility limits, and forecasting remaining wellbore life from which a reservoir management plan and wellbore management operational strategies were established. A key ingredient in the implementation of this plan and operational strategies involved a cooperative tool development with a major oil tool service company to repair casing "kinked" wellbores, as an alternative to re-drilling wells. This paper provides a case history describing the various synergistic reservoir and wellbore management activities designed to effectively mitigate subsidence-induced operational problems and the accompanying field benefits resulting from their implementation. INTRODUCTION The Sou...

Subsidence-Induced Casing Dogleg (SICDog) Remediation With an Innovative Hybrid Milling System

“…Subsequently, different types of subsidence-induced deformation were noted, such as compressional buckling and the dogleg category due to casing shear 2 . There was some reported activity to monitor and remediate doglegs in the early stages of dogleg formation before the dogleg began to reduce wellbore utility 3 . Efforts to further characterize and remediate doglegs appear in the literature later 4 .…”

Casing Shear: Causes, Cases, Cures

“…[3][4][5][6][7][8][9] Compaction is a volume diminution of the reservoir induced by a reduction in po, usually associated with depletion. The pressure decrease causes an increase in the grain-to-grain forces, and reservoir compaction occurs as these contacts compress or crush.…”

Field-Scale and Wellbore Modeling of Compaction-Induced Casing Failures

“…Such tools are capable of measuring the inclination of the casing in shear-damaged intervals, this inclination has been referred to as the ''kink angle.'' 12 The lateral offset of the casing from above to below the shear interval can also be measured, and the geometry of the deformed casing can be resolved. The computed deformed casing geometry is compared to measurements from a casing log in Fig.…”

“…A method of damage repair proposed in Ref. 12 involved reaming the damaged section of casing to reduce the curvature of the sheared casing, thus enabling the passage of through-casing tools after the repair. Under-reaming the hole during drilling was proposed in Ref.…”

“…It has been well documented that reservoir compaction can cause casing failures by tension, buckling, collapse, and shearing. In particular, compaction-induced shearing causes severe localized deformation of casing over small lengths, often less than 10 ft. [5][6][7][8][9][10][11][12][13] The interaction of soft rock with casing governs the geometry of the deformed casing. If effective and lasting damage mitigation and failure prevention measures are to be designed and implemented, then understanding the mechanisms of shear-induced casing damage is required.…”