Pressured Mud Cap Drilling (PMCD) is an advanced technique to control wells which encounter heavy mud losses and has been applied on onshore and offshore wells with surface wellheads. The key to successfully apply the technique is the use of a Rotating Control Device (RCD), which is a technology taken from Under Balanced Drilling (UBD). PMCD has not been applied to date on subsea wells as rigging up the RCD on the drilling riser brings additional challenges compared to surface wells. Three subsea wells were drilled Offshore Sarawak, utilizing the PMCD technique. A detailed review was made to rig up an RCD on the drilling riser of a Semi-Submersible drilling rig. The riser between the subsea BOP and the RCD at surface formed a low-pressure system to control the well. The first 2 wells did not see any losses but on the 3rd well, total losses occurred and the system was activated. The final result gave reason to look back on a successful operation but also good learnings were made for future operations. Introduction Since the 1970's, Shell Malaysia has drilled more than 150 wells into the carbonate structures offshore Sarawak. These carbonates normally exist of reef build-ups, many of them are more than 1000 feet high, are sometimes charged with gas and can be over-pressured up to 1300 psi. The biggest hazard when drilling through these carbonates are total losses, which historically has occurred in one out of six wells drilled. These losses are mainly caused by karsts, a common geological feature in the Sarawak carbonates. Severe well control situations have been the result of these losses, where total losses sometimes lead to the entire well being evacuated to gas. Measures to control these losses were previously managed by placing Diesel Oil Bentonite (DOB) plugs and in the later years more sophisticated fiber cement plugs were used. These methods resulted in the additional risk of getting the drill string plugged and stuck creating even worse well control situations. In year 2000, together with the development of more reliable Rotating Control Device (RCD), Pressured Mud Cap Drilling (PMCD) techniques were explored on the platform wells with Tender Assist and Jack-Up rigs. PMCD has since then evolved to be the safest method to control the carbonate losses. "There are two types of people who have applied PMCD; the ones who planned for it but never needed it and the ones who did need it but never planned for it". With the increasing amount of horizontal wells with lower overbalance compared to vertical or deviated wells, no significant losses have been recorded in some 20 carbonate wells drilled since year 2000 offshore Sarawak. With the increasing activity of subsea developments and still having some carbonates unexplored, the idea of taking the PMCD set-up from Tender Assist - and Jack-Up rigs to Semi Submersible Drilling rigs was born. The barrier of doing this was lowered due to the pioneering of other technologies, e.g. Under Balanced Drilling (UBD) and Surface BOP (SBOP) for deepwater drilling operations in Shell Malaysia. Installing a RCD on top of the drilling riser could be accomplished relatively easy based on the learnings of these technologies. Additionally, equipment was provided by a contractor who had experience with a similar project offshore Brazil, where an RCD was installed on top of a drilling riser. Pressured Mud Cap Drilling Technique Pressured Mud Cap Drilling (PMCD) is a method to control wells with heavy losses. When drilling conventionally, drilling fluid with a slightly higher hydrostatic head (300 psi) than reservoir pressure is used to keep hydrocarbons from flowing. When losses occur and the fluid level cannot be maintained at surface, the hydrostatic head will eventually drop to balance reservoir pressure at the loss zone. When this happens the wellbore pressure at the top of the Carbonate can be several hundred psi below the reservoir pressure. With such large under-balance and permeable formation, gas starts flowing into the well immediately after that the level has dropped down. Primary well control can now only be maintained by filling up the well with mud at a rate, which exceeds the gas percolation rate (Figure 1).

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractFollowing encouraging results of Under-Balanced Drilling ("UBD") applications in the North Sea and onshore Canada, Shell Malaysia Exploration and Production ("SM-EP") embarked upon the application of this technology in a shallow clastic oil field in offshore Sabah. Relatively little information is available in the public domain regarding the effectiveness of UBD in clastic oil reservoirs. This paper provides factual evidence relevant to the assessment of UBD-induced added value. The paper also provides a comparison between the cost and benefit of UBD with that of Under-Balanced Perforating ("UBP") in a two-well trial.Every pressure regime, reservoir fluid type, geological circumstance, etc, requires a specific operational configuration custom made for the situation at hand. This is a major source of UBD-induced incremental cost. Different reservoirs require different UBD configurations so analogies that assist the business case of a UBD project are currently limited and are difficult to find. This was the first offshore application of crude oil and hydrocarbon gas injection as drilling fluid in jointed pipe operations. A description of the incentives and risks of our specific geological circumstances is provided. Detail will be provided regarding our UBD design, main operational-risk mitigation measures, and the strategy used to appraise the added value of UBD. The complexities, incentives, and pitfalls of our UBD strategy will be chronicled. The initial results of this first-ever UBD trial within SM_EP will be published, along with the lessons that we have learned.

Sarawak Shell Bhd operates the Shallow Clastics field, which targets two shallow gas-bearing reservoirs, H1 and H2. An early appraisal well had been drilled deviated, and 9–5/8-in. casing was used. A commingled upper completion and a sand-face completion using large-OD expandable sand screens through both targets was used. Upon completion, the well was cleaned up through a temporary well clean-up and test facility. The purpose of the well was to test productivity and evaluate the integrity of the downhole sand-exclusion installation. Fines production, possibly due to the failure of the sand exclusion method, steadily increased to the extent that the well was deemed unproducible to the facilities. Due to the high fines produced from this first well, a re-evaluation of the sand exclusion method was undertaken before development of the remaining field. The re-evaluation included more extensive core analysis and reviews of the types of sand-face completions suitable for development of the H1/H2 reservoirs. This evaluation enabled the operator and a service/engineering company to develop an innovative sand-exclusion method that combined several new technologies. This paper discusses the evaluation and the four wells that have been completed to date with this new sand-exclusion method and the well configuration to address the completion needs. The field implementation of the design, key success factors and results will also be summarized. Introduction Sarawak Shell's Shallow Clastics field consists primarily of two shallow gas bearing reservoirs, H1 and H2, at approximately 2,650 ft TVD. These reservoirs are laterally extensive, covering an estimated area of 200 square km with estimated gas-in-place (GIP) in excess of 2 Tscf. The reservoirs are made up of a sequence of highly laminated sand and shale deposits with significant sand-size variability and high fines content, Figure 1. The unconsolidated nature and high fines content make downhole sand exclusion mandatory to maintain production. An early appraisal well was deviated and cased through both the H1 and H2 reservoirs. The well had been completed with 9–5/8-in. casing, expandable sand screens across both reservoirs, and a commingled upper completion. Upon completion, the reservoirs were cleaned up through a temporary well clean-up and test facility to test the productivity and evaluate the integrity of the downhole sand-exclusion method. Fines production, possibly due to the failure of the expandable sand screen, commenced almost immediately and steadily increased to the extent that the well could no longer be produced. Because of the results in the first appraisal well, the operator initiated a re-evaluation of the field development plan and well concepts. This re-evaluation consisted of additional core sampling and a review of the well types suitable for the H1/H2 reservoirs. The analysis of the core sample from F13–6 showed sand grain sizes of D50 80–220 µm, which were smaller than expected, Figure 2. The Uniformity Coefficient, given by the D40/D90 ratio, varied between 1.5 and 34, which indicated that the formation sands were highly non-uniform. Another evaluation was performed to look at the Sorting Coefficient, given by D10/D95, which varied between 2.5 to 130, giving further proof that the formation sands contained highly nonuniform grain sizes, Table 1. The fines content in these reservoirs reached 34%, which is considered high for attempting to produce with minimal-to-no solids production. The original wellbore selection consisted of deviated wellbores with stand-alone or expandable screens across the openhole H1 reservoir. Following the well testing results on the appraisal well, a full qualitative analysis of the well type suitable for these reservoirs was completed. The analysis looked in depth at other sand exclusion methods available, including traditional openhole horizontal gravel pack (OHHzGP), openhole horizontal gravel pack with concentric annular packing (CAPS), frac and pack, internal gravel packs (IGP), and expandable sand screens.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe Shallow Clastics Field, operated by Sarawak Shell, targets two shallow gas-bearing reservoirs, H1 and H2, at approximately 2,650 ft true vertical depth (TVD). An appraisal/early-producer well with a deviated wellbore was drilled through the H1, H2 targets, and a completion design consisting of a cased and perforated commingled completion inside 9-5/8-in. casing was implemented. The sand-face completion design consisted of a large-OD expandable sand screen with 150 micron weave across the 2 zones. Upon completion, the reservoirs were cleaned up through a temporary well clean-up and test facility to test productivity and evaluate integrity of the downhole sand-exclusion installation. Fines production, possibly due to a failure of the expandable screens, commenced almost immediately upon well bean-up and steadily increased to the extent that the well was deemed unproducible to the facilities.The failure of the first well caused a re-evaluation of the sand exclusion method employed, which included more extensive core analysis and the completion types that would be suitable for development of the H1/H2 reservoirs. From this review, the operator and a service/ engineering company were able to develop a sand-exclusion method that combined several new technologies needed to effectively complete this reservoir.To date, four wells have been completed with the new well configuration and sand-exclusion method chosen to address the completion needs. These have been tested, and to date, have proven to be operating satisfactorily. This paper will review the evaluation that led to the sandface completion design, the field implementation of the design, and the key installation success factors that were required. Results and a summary of best practices from the initial installations will also be summarized.

Summary The Shallow Clastics field operated by Sarawak Shell primarily targets two shallow gas-bearing reservoirs, H1 and H2, at approximately 2,650 ft truevertical depth (TVD). An appraisal, early-producer well was drilled with adeviated wellbore through the H1/H2 targets, and a completion design consisting of a cased, perforated, and commingled completion inside 95/8-in. casing was implemented. The sandface-completion design consisted of a large-outside-diameter (OD) expandable sand screen with a 150-µ-weave opening across the two zones. Upon completion, the reservoirs were cleaned up through a temporary well-cleanup and test-facility to test productivity and evaluate the integrity of the downhole sand-exclusion installation. Fines production, possibly caused by a failure of the expandable screens, steadily increased to the extent that the well was deemed unproducible to the facilities. A re-evaluation of the sand-exclusion method that included more extensive core analysis and the types of wells that would be suitable for development of the H1/H2 reservoirs was initiated. From this review, the operator and a service/engineering company were able to develop an innovative sand-exclusion method that combined several new technologies. To date, four wells have been completed with the new sand-exclusion method and well configuration chosen to address the completion needs. These have been tested and, to date, have proved to be operating satisfactorily. This paper will review the evaluation that led to the revised sandface-completion design, the field implementation of the design, and the key installation success factors that were required. Results and a summary of best practices from the initial installations also will be summarized. Introduction Sarawak Shell's Shallow Clastics field consists primarily of two shallow gas-bearing reservoirs, H1 and H2, at approximately 2,650 ft TVD. These reservoirs are laterally extensive, covering an area of 200 km2 with an estimated gas in place (GIP) in excess of 2 Tcf. The reservoirs are made up of a sequence of highly laminated sand and shale deposits with significant sand-size variability and high fines content. Being highly unconsolidated, downhole sand exclusion is mandatory. The primary drive mechanism is a depletion drive based on the weak aquifers seen in existing fields in the area. The Shallow Clastics reservoirs overlay deeper Central Luconia carbonate gas reservoirs, which are already on production with further fields in development; therefore, a gas-processing and gathering system was already in place. Gas from all of these fields is produced to the Malaysian Liquified Natural Gas (MLNG) plants at Bintulu, East Malaysia. Production from the Shallow Clastics field is intended to counteract decline from other field sand is critical to maintaining the security of the supply to MLNG. Significant log data (Fig. 1) on the Shallow Clastics field were gathered from the appraisal and development wells of the deeper carbonate gas reservoirs; however, core data were limited to what could be generated from a single poor-quality core from E11-SC1. A dedicated Shallow Clastics appraisal/early-producer well (E11-SC2) had been drilled with a deviated wellbore through the H1/H2 targets, and a completion design consisting of a cased and perforated commingled completion inside 95/8-in. casing had been implemented. The sandface-completion design consisted of a large-OD expandable sand screen with a 150-µ-weave opening across the two zones. Upon completion, the reservoirs were cleaned up through a temporary well-cleanup and -test facility to test productivity and evaluate integrity of the downhole sand-exclusion installation. Fines production, possibly caused by a failure of the expandable screen, commenced during the cleanup and steadily increased to the extent that the well no longer could be produced.