Underbalanced Horizontal Drilling: A Field Study of Wellbore Stability in Brazil

Underbalanced Horizontal Drilling: A Field Study of Wellbore Stability in Brazil Jose L. Falcao; Jose L. Falcao Petrobras S.A Search for other works by this author on: This Site Google Scholar Carlos F. Fonseca Carlos F. Fonseca Petrobras S.A Search for other works by this author on: This Site Google Scholar Paper presented at the SPE Asia Pacific Oil and Gas Conference and Exhibition, Brisbane, Australia, October 2000. Paper Number: SPE-64379-MS https://doi.org/10.2118/64379-MS Published: October 16 2000 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Get Permissions Search Site Citation Falcao, Jose L., and Carlos F. Fonseca. "Underbalanced Horizontal Drilling: A Field Study of Wellbore Stability in Brazil." Paper presented at the SPE Asia Pacific Oil and Gas Conference and Exhibition, Brisbane, Australia, October 2000. doi: https://doi.org/10.2118/64379-MS Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentAll ProceedingsSociety of Petroleum Engineers (SPE)SPE Asia Pacific Oil and Gas Conference and Exhibition Search Advanced Search AbstractThis paper discusses the design and wellbore stability considerations to drill four underbalanced horizontal wells in a mature, pressure-depleted and high permeability reservoir in the onshore Estreito field - Northeast of Brazil. To do so, it was determined the minimum mud weight that produced the minimum ECD below reservoir pressure, but above the lower collapse pressure, that keeps the wellbore integrity. For that, two approaches were employed: an in-house linear elastic stability simulator, named SEST, and a poroelastic simulator that takes into account the plastic yielded area around the wellbore.The main operational aspects related with stability of the first two horizontal underbalanced wells are also discussed. Finally, the results indicate that the methodology adopted in the design was successfully applied in the field.IntroductionThe Estreito field in Rio Grande do Norte - Northeast of Brazil, was discovered in 1982 and since then 764 wells have already been drilled by Petrobras in the area. Trying to produce the oil below the A u River, not accessible for vertical and non-economic for directional, four horizontal wells were drilled between 1995 and 1998. In those wells the Overbalanced Drilling (OBD) technique was employed.For this year (2000), Petrobras is planning to drill four more horizontal wells, but this time, following the world tendency, employing the Underbalanced Drilling (UBD) technique. In Fig. 1 are shown the location of the Estreito Field and the position of the horizontal wells.Geological CharacteristicsThe Estreito Field is localized in the onshore portion of the Potiguar Basin. The main reservoir in the field, is a heterogeneous and low consolidated sandstone of fluvial origin interbeded with claystone stringers. This reservoir has high porosity and high permeability. In addition, some wells presented sand production problems. Table 1 shows a summary of the main reservoir characteristics.The oil produced has high viscosity >1000 cp) in bottomhole conditions. The vertical wells have average oil production of 6 m3 /day (36.8 bbl/day) with steam injection and 2 m3 /day (12,6 bbl/day) without. The average initial BSW was 40% and today is 80%.Underbalanced Drilling ConceptThe Underbalanced Drilling (UBD) emerged as a distinct technique in the late 1980 s in the USA and Canada. Since then, it has gained acceptance among the operators and many wells have been drilled around the world employing this tecnology with varying degrees of success. The main characteristic of the UBD is to drill a well with an intentionally designed Equivalent Circulation Density (ECD) lower than the formation pore pressure. As a result, the formation fluids will be produced while the drilling progresses.When properly designed and executed, the UBD offer improvements over the conventional OBD technique, such as(1,2) :minimizes formation damage and improve well productivity,increases rate of penetration and extends drill bit life,allows better characterization and reservoir evaluation while drilling,eliminates lost of circulation and differential sticking,provides an alternative method of well control.Our goal in employing this technique in Estreito field is to minimize formation damage and improve well productivity.As a disadvantages we can cite some(1,2) :increased costs due to additional equipments required,complexity of the operations with a well alive,safety considerations,decrease of the borehole stability due to reduced bottomhole pressure. Keywords: spe 64379, in-situ stress field, upstream oil & gas, simulator, drilling operation, fonseca, horizontal well, plastic yelded area, society of petroleum engineers, wellbore stability Subjects: Wellbore Design, Drilling Operations, Pressure Management, Reservoir Characterization, Wellbore integrity This content is only available via PDF. 2000. Society of Petroleum Engineers You can access this article if you purchase or spend a download.

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