TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe objective of this paper is to highlight the techniques used during a recent workover program to alleviate sustained casing pressure in a Gulf of Mexico field. Discussion will include cement and workover fluid programs, hole preparation before milling and cementing operations, and improved milling procedures.

Production and surveillance engineers need practical models to help balance out the reward of maximizing production and the risk of ramping-up the well too much that damages the completion. This paper presents a well flux surveillance method to monitor and ramp-up production for openhole stand-alone screen (OH-SAS) completion that optimizes production by considering risks of production impairment and screen erosion failure. The flux surveillance model for OH-SAS assumes the filter cake from drilling operations does not cleanup uniformly during fluids unloading and production. This leaves pinholes on the filter cake that cause concentrated flows. The flux model contains three components: (a) capture and describe input properties of pinhole, (b) link completion pressure drop of flows across filter cake region and through pinholes to surveillance results from pressure transient analyses, and (c) distribute fluxes in the SAS wellbore. The model uses three input parameters to describe the pinhole diameter and internal filter cake properties. They are determined as a system utilizing the laboratory return permeability test, computerized tomography scans of test samples, and computational fluid dynamics simulations. The completion pressure drop incorporates radial and hemispherical flows and captures the compounding skin effects of pinholes with internal filter cake. Flux distributions are modeled as a network system. This contains branches and nodes that incorporate radial and vertical flow resistances in the annular region of SAS. Application of filter cake properties and pressure transient analysis data showed the completion pressure drop as a function of flow rate is non-linear and higher with pinholes than without pinholes. By not incorporating pinholes in surveillance, operations can potentially limit ramp up when the completion pressure drop in the field is higher than predicted. Results from the network model showed the largest radial screen impingement velocity is at the top section of screen. The axial annular flow velocity or scouring velocity is two orders of magnitude larger than the screen impingement velocity. This warrants further considerations of wellbore enlargement and screen scouring erosion mechanisms due to the high axial annular flow.

The following will outline the Medusa Field development and completion design process highlighting an integrated approach between engineering disciplines and service providers to exploit the enormous amount of exploratory well data. The Medusa development, located in Mississippi Canyon blocks 538 and 582 offshore Louisiana, is a truss SPAR allowing for both dry tree production and multiple subsea tiebacks.A field overview from a geological and reservoir perspective, along with the drilling and field development considerations, will be summarized. The initial phase of the Medusa truss SPAR development includes ten compaction-tolerant FracPac completions in six dry-tree wellbores.Phase II wells included the drilling of two subsea tiebacks.One was drilled and deemed uneconomic while the second, Medusa North, was completed and tied back in early 2005. The paper will show how the information gathered during the drilling phase was applied to the completion design to ensure long-lasting, reliable and profitable wells. Introduction Design of deepwater completions requires a vast amount of planning and communication between all involved engineering disciplines. Bridging the gap between petrophysical, drilling, completions, and operations is imperative to obtaining project profitability through efficient, long-term and robust completions. Mechanical integrity is crucial to any completion design.Deepwater and subsea completions command very high production rates and can require fewer wellbores to develop a field.Add to this the high cost of well intervention and efficient, dependable wells with stacked pay horizons become the primary driver to economic deepwater Gulf of Mexico field development. The quality of a deepwater completion relies heavily on the proper use of reservoir data gathered during the drilling phase.Since it has a direct bearing on the efficiency of the completions, accurate analysis and use of this reservoir data must occur subsequent to the drilling phase.In particular, fluid samples, core samples, and logging data are all imperative. Field Overview The Medusa development, under Mississippi Canyon blocks 538/582 in the Gulf of Mexico, is about 100 miles south of New Orleans, Louisiana in about 2,200-ft of water (Fig. 1). The Medusa prospect originated from the drilling of two exploratory wells from a semi-submersible rig beginning in August 1999.These wells were sidetracked to further delineate the field and gather valuable core, fluid and logging data.Upon drilling of the discovery wells, an evaluation period followed in which economic decisions were made. Once field development was sanctioned, a development drilling program was initiated.Simultaneously, the design and fabrication of the truss SPAR production facility began. Medusa Field Development Timeline 08/99 - Spud Discovery Well 10/99 - Discovery Announced 05/00 - Delineation Drilling Complete 03/01 - Contract Awarded for Floating Production System 07/01 - Development Drilling Begins 03/02 - Development Drilling Complete 02/03 - Hull Installation 05/03 - Topsides Installation 07/03 - Topsides Commissioned 09/03 - Initial Completion 11/03 - First Oil The time from the end of the drilling phase to the commissioning of the production facility was used to analyze all available reservoir data and explore various completion techniques.From this analysis, mechanically sound, high-rate completions were designed and a reservoir depletion plan was developed to efficiently produce the hydrocarbon reserves from the multiple sands in the field.

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Summary Well surveillance requires practical models to balance the reward of maximizing production with the risk of ramping up production too much, which damages the completion. In this paper we present a method to monitor and ramp up production for openhole standalone screen (OH-SAS) completion. The objective is to optimize production using pressure transient analyses to assess the completion impairment and failure risks during the production ramp-up process. The flux model incorporates filter-cake pinholes, which are formed from nonuniform deposition and cleanup of filter cake during drilling and completion operations. Pinholes cause concentrated fluxes and increase completion failure risks. The method comprises three components, which are (1) determine pinhole properties from laboratory tests, (2) relate completion pressure drop of production through pinholes to pressure transient analyses, and (3) distribute fluxes in the standalone screen wellbore. Examples are presented and show that the completion pressure drop as a function of flow rate is nonlinear and higher with pinholes than without pinholes. By not incorporating pinholes, operations can potentially limit ramp-up. Flux distribution examples show that the largest impingement or radial velocity is at the top section of screen. The axial annular flow velocity or scouring velocity is two orders of magnitude larger than the screen impingement velocity. An integrated flux surveillance method for OH-SAS completion is presented for field applications.