Heather Field Research Articles

The value of core in mature field development – examples from the UK North Sea

Abstract Core-based studies have had material impacts on the understanding of a number of late-life, mature North Sea Brent Group hydrocarbon reservoirs. These studies have included sedimentological, diagenetic and reservoir quality focused evaluations of core. The primary objective of the studies has been to improve conceptual and qualitative models that can be utilized in reservoir modelling and also for infill drilling and well workover evaluations. Most of these studies have been undertaken on old core samples collected in the 1980s and 1990s. Two case studies are described here that provide examples of the utility of core in mature fields. (1) Heather Field calcite: to quantitatively assess the distribution of calcite cements and their impact on hydrocarbon volumes and reservoir quality distribution in Brent reservoirs. (2) Thistle Field Etive Formation barriers and baffles: to characterize and describe the origin and distribution of low-permeability intervals within the Etive Formation reservoir. These two studies used a wide variety of core-based techniques including core logging and description, optical microscopy and petrographical studies, isotope analyses, X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) (FEI Company analysis tool and software, QEMSCAN)-based mineralogy, portable-X-ray fluorescence (XRF), NDTr and Thermo Scientific Inc. NITON TM operational software (NDT) geochemical analysis, as well as image analysis of grain size and texture. These data were then integrated with other subsurface datasets, such as well log, seismic data and well performance data, in order to address the specific reservoir challenge. These new and focused reappraisals of core demonstrate the dual value of core-based studies, which can: improve the understanding of producing hydrocarbon reservoirs, leading to improved productivity and recovery. Core is a full asset life-cycle resource and provides critical insight at all stages of field maturity as production behaviour changes and alternative development strategies are considered; further our general knowledge and understanding of clastic sedimentology and diagenesis using rich and diverse core-based datasets backed up by substantial well log and seismic datasets.

A renewed look at calcite cement in marine-deltaic sandstones: the Brent Reservoir, Heather Field, northern North Sea, UK

Abstract Wireline and seismic acoustic impedance imaging show that the marine part of the clastic Brent Group reservoir in the Heather Field, northern North Sea, contains much calcite cement in the flank parts of the structure. The non-marine Ness Formation and crest parts of the structure contain negligible calcite cement. This localized calcite cement has led to relatively poor reservoir performance since first oil in 1978, although a new suite of wells has boosted production with plans to keep the field active until 2030. Understanding the origin and distribution of calcite cement would help the development of more realistic reservoir models and boost production rates through optimum well location. We have thus used a suite of techniques, including standard point counting, SEM-EDS mineralogy, BSE microscopy, fluid inclusion thermometry and stable isotope analysis, to develop new and improved models of calcite distribution. Calcite seems to have attributes of both early and late diagenetic cement. A 30–40% intergranular volume in calcite cemented beds seems to support pre-compactional growth but high-temperature fluid inclusions and the presence of primary oil inclusions suggest late growth. Much calcite may have developed early but it seems to have recrystallized, and possibly undergone redistribution, at close to maximum burial or had a late growth event. Calcite cement probably originated as marine-derived micrite, bioclasts or early marine cement but adopted the isotopic characteristics of high-temperature growth as it recrystallized. Quartz grains have corroded outlines in calcite-cemented areas with one sample, with 79% calcite cement, displaying signs of nearly total replacement of quartz grains by calcite. The flank localization of calcite cement remains to be explained, although it could be due to primary depositional factors, early diagenetic loss of calcite from crestal regions or late diagenetic loss of calcite from crestal regions. Controversially, the growth of calcite seems to be associated with quartz dissolution, although the geochemical and petrophysical cause of this remains obscure. Diagenetic loss of quartz from sandstones cannot easily be explained by conventional modelling approaches and yet seems to be an important phenomenon in Heather sandstones.

The Heather Field, Block 2/5, UK North Sea

abstract The Heather oil field is located in Block 2/5 in the Northern North Sea. Oil is produced from sandstones of the Middle Jurassic Brent Group. at depths between 9500ft and 11600 ft below sea level. The field has been in production for over 20 years, and to date 120 MMSTB of oil have been produced out of an oil-in-place volume of 464 MMSTB. Although approaching non-commercial flow rates, an ambitious programme of field re-evaluation has been conducted since 1997 to identify remaining infill potential, and to investigate the development potential of satellite accumulations. New 3D seismic surveys shot in 1995 and 1997 have been combined to produce a continuous top reservoir map of the main field and adjacent satellite structures. The new mapping and an updated reservoir description were integrated with reservoir simulation models to identify zones of unswept oil. Main field infill projects have been identified which target the unswept oil, allowing extension of field life to be planned in conjunction with satellite field development. An additional 57 MMSTB of recoverable oil are expected to be produced from Middle Jurassic reservoirs in the main field and in satellite areas.

Innovative use of petrophysics in field rehabilitation, with examples from the Heather Field

The Heather oil field is located in the Northern North Sea and is operated by DNO Heather Limited. Oil is produced from sandstones of the Middle Jurassic Brent Group. Although approaching non-commercial flow rates, infill projects are under way which target unswept oil. At this late stage in field life, projects are typified by extracting as much new oil from the field as possible with minimal expenditure. These result in incomplete or degraded log data. This paper describes how the application of innovative techniques can replace data shortfalls, providing quality data without compromising budgetary constraints. Four infill wells were drilled during 2000 and 2001. Innovative petrophysical techniques have been used to enhance the electric log data gathered. Fuzzy logic techniques have been applied to predict reservoir permeability and choose perforating intervals. Some sections of the highly deviated wells were necessarily logged in sliding mode and fuzzy logic was also used to repair the resulting degraded log curve data. Following the infill well programme, field production has increased from 5000 BBL oil per day (BOPD) to 7000 BOPD. This success was partly due to the better location of wells, particularly 2/5-H62Y, because of the improved reservoir model resulting from these petrophysical techniques. The height above free-water level (HAFWL) was estimated across the Heather Field using the so-called FOIL function (bulk volume of water plotted as a function of HAFWL) ( Cuddy 1993 ). The FOIL function has given valuable insights into free-water level variation across the Heather Field and has improved water saturation modelling. A method is presented in this paper for geosteering using the FOIL function.

Winter population size and habitat selection of Crested Tits Parus cristatus in Scotland

Estimates of the number of winter social groups of Crested Tits in Scotland ranged from 2300 (95% CL 1300–3900) to 3300 (95% CL 2000–5200) during a survey over three winters in ancient native pinewoods and other woodlands. These represent a population of 5600–7900 birds after adjustment for incomplete counts of group sizes. Mean group densities were about ten times higher in ancient native pinewoods (9.0–10.3 km-2) than in other woodlands (0.7–1.3 km-2) which comprised largely planted Scots Pine, Lodgepole Pine and Sitka Spruce. Thus, 35% of the Scottish population of Crested Tits occurred in ancient native pinewood, which comprises only 4.7% of the woodland. Crested Tits were associated mainly with Scots Pine, but were also seen in Lodgepole Pine, Norway Spruce, larch, Rowan, Alder and birch. The group densities within the stands of Scots Pines in ancient native pinewoods were 10.4–12.3 km-2 and 1.2–2.4 km-2 in Scots Pines in other woodlands. Within ancient native pinewoods, they preferred stands with a high proportion of Scots Pines, and particularly those with older trees. In other woodlands, there was again a preference for stands with a high proportion of Scots Pines, and Heather was also selected. Crested Tits will continue to benefit from the planting of Scots Pines, and if the woods develop a Heather field layer. However, they will not benefit from spruce plantations.

Water Shutoff in the North Sea: Testing a New Polymer Gel System in the Heather Field, UKCS Block 2/5

Summary A new polymer gel system developed for high-temperature applications was successfully employed on Well H-43 of the Heather Field to isolate a high-rate water production zone. The high-temperature, organic polymer gel system has demonstrated long-term stability when mixed with seawater at temperatures as high as 350°F. Gel times can be delayed, allowing a large volume of polymer gelant to be placed. For Well H-43, 1,095 bbl of gelant were pumped through 1½-in. coiled tubing into a 15-ft layer of the Brent Group. The treatment increased oil production by 300 B/D and decreased water production by 2,290 B/D. A production log run 8 months later confirmed effective isolation, allowing the lower Brent to produce.

The Heather Field, Block 2/5, UK North Sea

Abstract The Heather Oil Field is located at the western margin of the East Shetland Basin, in the northern North Sea, and is operated by Unocal UK Ltd. Oil is trapped in Middle Jurassic Brent Group sandstones below 9500 ft TVSS in a highly-faulted reservoir that has undergone considerable diagenetic modification. The field was declared commerical in 1974, began producing in 1978 from a single platform and has recovered 84 MMBBL of oil to date through primary and secondary recovery methods. Ultimate reserves are estimated to be 100 MMBBL of oil.

Roberts, Ivan, Graham Love, Heather Field, and Nico Klijn. U.S. Grain Policies and the World Market. Policy monograph no. 4, Australian Bureau of Agricultural and Resource Economics. Australian Government Publishing Service, Canberra, 1989, xvii + 286 pp. (Available in the United States and Canada from ISBS Inc., 5602 NE Hassalo St., Portland OR, 97213–3640.) Price unknown

Roberts, Ivan, Graham Love, Heather Field, and Nico Klijn. <i>U.S. Grain Policies and the World Market</i>. Policy monograph no. 4, Australian Bureau of Agricultural and Resource Economics. Australian Government Publishing Service, Canberra, 1989, xvii + 286 pp. (Available in the United States and Canada from ISBS Inc., 5602 NE Hassalo St., Portland OR, 97213–3640.) Price unknown

Ibsen and the Irish Theatre

The Irish Literary Theatre, from which a new Irish theatre was to develop, came to birth at the very point when Ibsen was about to depart from the European theatrical scene. His last play, When We Dead Awaken, appeared in 1899, the year in which Yeats's The Countess Cathleen and Edward Martyn's The Heather Field were produced in Dublin. They were the first fruits of the resolve taken by the two playwrights, with Lady Gregory and George Moore, to ‘build up a Celtic and Irish school of dramatic literature’ and they offered decidedly different foretastes of what that ‘school’ might bring forth. Yeats declared himself an adherent of a poetic theatre that would use fantasy, vision and dream without regard for the limits set by the realistic convention. Martyn, on the other hand, was clearly following Ibsen in his careful observance of day-to-day probability. The central symbol of his play, the heather field, represents an obscure psychological process which might have received more ‘inward’ treatment. But instead it is fitted into a pattern of social activities in something like the way of the prosaically functional but symbolic orphanage in Ghosts.

Geochemical Evidence for the History of Diagenesis and Fluid Migration: Brent Sandstone, Heather Field, North Sea

The diagenesis of Brent Group sandstones at Heather Field was studied to reconstruct time-dependent variations in reservoir quality, hydrodynamic history, and oil emplacement. Depositional facies, isotopic and trace-element composition of authigenic minerals, and present-day formation-water chemistry indicate several major changes in porewater chemistry related to both gravitational and compactional flow systems that significantly impacted diagenesis. Early cementation by calcite was related to influx of meteoric water and completely occludes porosity in certain areas of the Field, especially in lower reservoir zones. Geochemical, petrographic, and structural evidence indicate that average calcite precipitated at low to moderate temperature from reducing isotopically-depleted water having high levels of radiogenic Sr (40°–50°C, δ 18O = −4 to −6‰, 87Sr/86Sr > 0·71). A major period of kaolinite precipitation and feldspar dissolution followed calcite cementation. The isotopic composition of pore-filling kaolinite shows Field-wide uniformity (δ 18O average 13·8‰, δD average −53·2‰), suggesting thorough flushing of the reservoir by meteoric water and precipitation at low to moderate temperature (45°–60°C). Tectonic, burial, and thermal histories suggest that meteoric flushing occurred during the late-Cimmerian sea-level low, possibly in response to gravitational flow of meteoric water from exposed parts of the adjacent East Shetlands Platform. Illite and quartz diagenesis post-date kaolinite cementation, with illite K-Ar ages indicating precipitation through much of the Paleogene (55–27 Ma), coincident with migration of hydrocarbons from neighbouring sub-basins of the East Shetlands Basin. Illite stable isotopic data indicate precipitation in a system resulting from partial mixing of trapped meteoric pore-fluids with saline compaction water. The intensity of sandstone diagenesis is influenced by differences in the fluid migration history, content of detrital K-feldspar, and the time of hydrocarbon emplacement and results in spatial and temporal variations in reservoir quality.

Temporal and Spatial Variation in Diagenesis and Reservoir Quality: Brent Sandstone, Heather Field, North Sea: ABSTRACT

Brent Group sandstones in the Heather field show extreme inter- and intrafacies heterogeneity in reservoir quality as a result of diagenetic variation. Diagenetic patterns varied spatially and temporally as a result of variations in paleofluid chemistry, the time of hydrocarbon accumulation, and detrital grain composition. Important diagenetic cements are poikilotopic calcite, kaolinite, quartz, and illite. Geochemical, petrographic, and structural evidence indicate that calcite precipitated in the Late Jurassic (approximately 150 Ma) at a low temperature (40/degrees/-50/degrees/C), from reducing water of partial meteoric derivation (/delta//sup 18/O water = /minus/4 to /minus/6 /per thousand/ SMOW) that contained highly radiogenic strontium (/sup 87/Sr//sup 86/Sr > 0.71). Calcite distribution was partially controlled by local erosion of the Brent immediately following its deposition. Subsequently, a major period of kaolinite precipitation and feldspar dissolution occurred. Isotopic and tectonic/thermal history data suggest that these events were caused by thorough meteoric flushing (/delta//sup 18/O water = /minus/6 to /minus 8/ /per thousand/ SMOW) during the mid-Cimmerian sea level low (ca. 140 Ma), but not via recharge at the mid-Cimmerian unconformity immediately above the structure. Quartz precipitated as a result of feldspar dissolution, pressure solution, and fluid movement up fault zones over a long period of geologic time. Inmore » the vicinity of major faults, quartz fluid inclusions indicate invasion of hot, saline brines.« less

J. M. Synge on the Irish Dramatic Movement: an Unpublished Article

J.M. SyngeontheIrishDramaticMovement: an Unpublished Article ANN SADDLEMYER During the last week of April, 1906, the Irish National Theatre Society visited the north of England for the first time, performing in the Midland Theatre, Manchester, on April 23 and 24 before proceeding to Liverpool and Leeds. As the only Director based in Dublin, Synge had been taking increasing responsibility for Abbey Theatre business, and he arranged to accompany the players on tour. He appears to have written the following articleI while on the road or immediately after his return to Dublin, intending it for the Manchester Guardian. During the preceding year he had published two travel essays for the Guardian, and a series of twelve commissioned articles, illustrated by Jack B. Yeats, describing the congested districts of the west of Ireland. However, "The Dramatic Movement in Ireland" was apparently never published. Synge may well have had a hand in the writing of a more extensive illustrated souvenir programme describing the history of the movement and its major dramatists which was issued in May, however, when the company toured once again, with Synge in attendance, this time to Cardiff, Glasgow, Aberdeen, Newcastle, Edinburgh, and Hull under the management of Alfred Wareing.2 Although he frequently wrote articles, "paragraphs," and book reviews for the Manchester Guardian and elsewhere, this manuscript is a rare example of Synge's public assessment ofthe movement to which he contributed. An article published in L'Europeen, May 31 1902, entitled "Le Mouvement Intellectuel Irlandais," had included brief summaries of Yeats's Countess Cathleen and Edward Martyn's The Heather Field and a moving testimonial to the influence of the Gaelic League on the occasion of the first production of Douglas Hyde's play in Irish, The Twisting ofthe Rope: "On venait de sentir flotter un instant dans la salle I'arne d'un peuple."3 The historical facts Synge recounted then and here are familiar, including the anecdote about the "drunken wanderer" (James Joyce) asleep in the Camden Hall passage. But apart from brief comments in letters, this is the only indication we have of his commitment to what became known as Yeats's "Samhain principles," his response to the early productions of the Irish Literary Theatre, and his personal judgment of the landmarks and ideals of the early years of the Abbey Theatre. Synge: An Unpublished Article 277 THE DRAMA TIC MOVEMENT IN IRELAND by J.M. Synge The Irish plays which were produced in Manchester the other day are the result of a dramatic movement which has been going on in Ireland for some years. In 1899, Mr. W.B. Yeats, Mr. Edward Martyn, Mr. George Moore, Lady Gregory and some others founded the Irish Literary Theatre, and for the next three years, Irish plays were performed for one week annually in Dublin. The first performances took place in May 1899, when two remarkable plays were produced, The Heather Field by Mr. Edward Martyn and The Countess Cathleen by Mr. W.B. Yeats. They were played by English actors in a concert hall fitted up for the occasion, and The Countess Cathleen, a poetical and delicate play, suffered a good deal from bad scenery and a not very satisfactory delivery of the verse. One part however - that of the poet, Aleel- played by Miss Florence Farr was most musically spoken. The other play which had to do with modern life in Ireland was more easy to perform and was in every sense a success. The following year three plays were given, The Bending ofthe Bough by Mr. George Moore; Maeve by Mr. Edward Martyn; and The Last Feast of the Fianna by Miss Milligan. The Bending ofthe Bough had a sort of actuality which gave it a hold upon the audience; but the other two plays were not of much importance. Finally in the autumn of 1901, The Irish Literary Theatre wound up its career by giving two plays in the Gaiety Theatre, Dublin, Diarmuid and Grania, written by Mr. W.B. Yeats and Mr. George Moore in collaboration, and a small one-act comedy in Gaelic written by Dr. Douglas Hyde. The first play was acted by Mr. Benson's company and the second...

The Heather Platform Leg Repair

This case history reviews the analysis and repair of a corner leg of the Heather A platform; damage was caused by a foundation pile dropped during installation. The paper describes the stereophotographic and mechanical templating techniques used to verify shell deformations. The choice of a mechanical solution and the interface with module installation and commissioning are reviewed. Introduction The Heather field is located in Block 2/5 of the U.K. sector of the North Sea (Fig. 1). The Heather A platform is located at 0 degrees 56'22.53" longitude and 60 degrees 57'13.51 "latitude, approximately 100 km (64 miles) east of the northern end of the Shetland Islands in 143 m (470 ft) of water. The oil field was discovered in Dec. 1973, and a steel-pile-supported platform was selected to develop the discovery. With the availability of larger pile-driving hammers, the decision was made in the fall of 1975 to drive 1.52-m (60-in.) diameter piles. Each of the 24 piles [96 m long × 64 mm thick (315 ft × 2.25 in.) and 218 Mg (240 tons)] is made from a 64-m (210-ft) lead section with a 32-m (105-ft) extension welded offshore. During the offshore piling operations in the summer of 1977, one of the piles had been joined and was being held by the derrick barge in preparation for lowering to the seabed, then one of the shackles linking two sections of slings broke. The pile, laterally restrained in the guides, dropped more than 40 m (130 ft) in almost free vertical fall before hitting the jacket at the location shown in Fig. 2.The extent of the damage posed a potentially serious setback to field development. With the reduction of load-carrying capability of the platform, the complete module installation program was reanalyzed. The selection of the repair method was judged in line with performing the repair during the winter period. A limited number of modules were installed on the platform by mid-Oct. 1977, when the repair operation commenced from the semisubmersible vessel Treasure Hunter. The first phase of the repair was completed by mid-Jan. 1978, and the second phase from mid-April to the end of May finalized the repair.This paper traces the stages of design, repair, and techniques developed and appraises the interface with the remainder of the development. Description of Damage Initial impact of the pile was at the cone-shaped section of the "bottle" where the leg diameter increases from 2.5 to 5.7 m (8 to 18.5 ft). The pile glanced off the cone, buckling the 40-mm (1.625-in.) thick plate and punching a hole [approximately 1.25 × 1 m (4 × 3.5 ft)] in the cylindrical shell. At the junction of the cone and shell is a critical ring stiffener designed to contain the hoop stresses at this change in section. This ring stiffener was torn in two places, and the tongue section in between was bent downward. As the pile fell, it continued to dent the cylindrical shell up to 200 mm (10 in.) radially and caused further damage to a second lower ring stiffener. Denting of the vertical shell was caused over some 4.5 m (14.5 ft). JPT P. 569＾