The Second Long-Term Horizontal Well Test in Troll: Successful Production From a 13-in. Oil Column With the Well Partly Completed in the Water Zone

Abstract

Inspired by the success o f the first long-term test with a horizontal well on Troll1, a second long-term test was carried out in 1991. This 4 months long-term production test with an 800 m horizontal well was performed in a 13 m oil column sandwiched between a large gas cap and an active aquifer in the Troll West Gas Province. The horizontal section target depth was 1 m above the WOC, but approximately 25% o f the well trajectory was actually the WOC.The observed production data from the test were history matched with a numerical simulator. The effects o f various geological features on water cut and GOR development were studied, and several simulation models matching the production history were built. These models were used t o evaluate the effects on oil recovery o f various design parameters such as; length o f the horizontal section, completion depth, liner diameter and liner roughness.The production history indicated that inverse coning took place in the parts o f the well situated below the initial WOC. The history matching confirmed the results from the first long-term test, but also demonstrated the strong sensitivity o f history matching and long-term production predictions t o small changes in geological interpretations and t o frictional pressure loss in the horizontal section.Large upside potential was found in the Troll West Gas Province for longer horizontal wells, deeper completions and super-critical production.References and illustrations a t end o f paper 909

Three-dimensional modeling of clinoforms in shallow-marine reservoirs: Part 1. Concepts and application

“…These are observed at the outcrop to be laterally extensive (>80% areal coverage) along bedding planes and in a producing subsurface reservoir; their presence is marked by breaks in pressure and fluid saturation within seismically imaged clinoform sets (Morris et al, 2006;Hampson et al, 2014). Thus it appears probable that permeability barriers and baffles in the form of calcite-cemented concretionary layers occur along clinoforms in the Troll Field reservoir and could influence drainage patterns and recovery from the thin oil zone (Gibbons et al, 1993); this may have been recognized previously and shown to impact on well test interpretations (Lien et al, 1991;Haug, 1992). However, to date, the heterogeneity associated with clinoforms has not been explicitly included in reservoir or flow-simulation models of the Sognefjord Formation in the Troll Field.…”

Closed-Loop Feedback Control for Production Optimization of Intelligent Wells Under Uncertainty

“…However, it is recognized that they may have a significant impact on production. Lien et al (1991) and Haug (1992) presented the results of the first long-term well tests in the Troll West Oil province, and Troll West Gas province, respectively, and a number of dipping calcitecemented barriers were interpreted to explain the observed pressure responses.…”

**Comparative Aspects of Coning Behaviour in Horizontal and Vertical Wells

“…For cases where the reservoir has a moderate number of isolated layers, there may stilt be preferable opportunities for horizontal weNs, by using stepped, or multi lateral configurations, or by creating hydraulic fractures. A secondary consideration for choosing horizontal weUs (H\Vs) is in circumstances wbere vertical coning (or " cresting' describes better the shape of the fluid interface) may offer advantages in the critical rate at which a well can be operated to avoid breakthrough of gas from a gas cap, or water from a bottom aquifer, or both [4]. For example, operation of a field may have caused a gravity gas tongue to develop below a major shale in a reservoir zone, for which a horizontal lateral is to be drilled whose length, depth and flow rate should be designed to limit the timing and magnitude of gas breakthrough.…”