Traditionally, Non-Aqueous Fluids (NAF) have been used by a major operator to drill challenging wells in the Campos
Basin, Brazil. Significant advances in water based drilling fluid design in the recent years have allowed water-based drilling fluid performance to approach that of NAF. Exploration in the new frontiers and optimized development well projects in deepwater Brazil have required a different approach regarding drilling fluid design due long step outs, difficult well trajectory, and the possibility of drilling horizontal wells in one step, thus avoiding intermediate casing strings. Although NAF are an ideal candidate for those applications, environmental concerns and logistic demands are still an issue and alternatives should be considered.
HPWBM has been applied to replace NAF in some applications in deepwater and ultra deepwater (UDW) in the Campos Basin. This novel technology has been successfully applied to drill in UDW scenarios, reactive clays, dispersive shale, naturally micro fractured formation and horizontal wells. HPWBM characteristics are developed with: 1) A new generation of encapsulation polymers; 2) The use of amine chemistry to provide clay stability; 3) The application of novel sealing polymer for shale stability; and 4) Excellent mud lubricity characteristics.
The lessons learned, as supported by case histories and lab data have contributed to system modifications which have improved performance. This work has also identified attributes needed to complete a drilling fluid design for the difficult wells to be drilled in the new exploration and development areas. The evolution of HPWBM drilling fluid design will be discussed along with how decisions were made.
Today the industry is drilling more technically challenging wells difficult wells. Exploration and development operations
have expanded globally as the economics of exploration and production for oil and gas have improved with advancements in drilling technology. Advanced drilling operations such as deep shelf, extended reach, horizontal and deepwater are technically challenging, inherently risky and expensive. With consideration to reducing drilling problems such as torque and drag, stuck pipe, low rate of penetration and well bore stability; these wells are generally drilled with emulsion-based muds.
Nearly three quarters of the earth is ocean and a high prospect of hydrocarbon resources in addition to the other marine resources. That's why the industry is shifting from onshore drilling to offshore drilling. Published information indicates the presence of more than 20% of world's proven reserve in offshore geological structures. According to future production forecast of production reserves about 40-50% of future hydrocarbon recovery will be from offshore reserves. This is reflected by the increasing activity in the offshore environment with a gradual shift from shallow water drilling to deepwater drilling operations.
This scenario is particularly critical in the drilling exploration of offshore Brazil where the country faces the challenge of increasing oil production and reaching energy self-sufficiency within the next few years. Petrobras is well known for extended deepwater experience, however exploration in the new frontiers of ultra deep water face new challenges.
Elnaga, Aly Abou (Chevron San Jorge S.R.L.) | Almanza, Edgar A. (Halliburton Energy Services Group) | Batocchio, Marcelo Pavanelli (Halliburton Argentina S.A.) | Folse, Kent C. (Halliburton Energy Services Group) | Schoener-Scott, Martin F. (Halliburton Co.)
Chevron San Jorge S.R.L. operates in the Loma Negra area and El Trapial field located in the Neuquén Basin, Argentina.
El Trapial wells are characterized by stratified, shallow- to medium-depth reservoirs with permeabilities of 35md to 85md and porosities of 18 to 30%. The wells are completed in oil reservoirs that have been perforated using conventional methods, fracture stimulated to increase production, and later, completed with electro-submersible pumps (ESPs).
To effectively meet the operator's needs for a method that would help optimize well productivity, and at the same time, be cost effective without compromising the results of the operation, an improvement over traditional tubing-conveyed perforating (TCP) was required. A propellant-assisted (PA) perforating method that could optimize well productivity while maintaining stringent health, safety and environmental standards was proposed. The propellant-assisted perforating method uses standard perforating components and procedures, thus providing the same safety features available to the industry today when conventional TCP operations are used. The propellant is an oxidizer that creates carbon dioxide gas at extremely high peak pressures in the millisecond time regime to overcome in-situ stresses and create perforation breakdown and mild fracturing near the wellbore.
This paper will focus on two case histories describing the methods and improved results obtained from the application of the propellant perforating technique.
The information in this paper will verify that the technique was capable of satisfying the operational challenges in these reservoir types. Instrumental in the success of the propellant-assisted perforating methodology was 1) the proper screening of candidate wells, 2) good pre-job design modeling, and 3) adherence to industry accepted best practices with constant communication.
El Trapial Field was discovered in 1991. It is part of a near-shore, shallow marine environment. It is situated in the Neuquen Basin (Fig. 1) in the Northeast quadrant of the Neuquen Province of Argentina. The main reservoir in the El Trapial field is the Lower Troncoso where 57% of the total reserves reside. It is composed of sandstone in eolian faces, of a medium-grained clast-supported texture, scarce matrix and dolomite cement, with good to very good porosity and permeability.
New well logs were run, and when they identified increasing water cut in the production, Chevron decided to try a new technology to perforate these wells rather than the conventional tubing-conveyed perforating (TCP) techniques previously used followed by conventional hydraulic fracturing.) This new technology chosen included propellant sleeves with the TCP guns, which was capable of increasing the exposure area (fissures) created by the gas (CO2) in the propellant sleeves.
Loma Negra field complex on the Rio Negro Norte Block in southeastern Neuquen has hosted several discoveries since opening of Loma Negra field in 1997. Loma Negra, with reserves of at least 240 million bbl. could be one of Argentina's top producing fields of this decade. The formation is a sandstone called Punta Rosada with permeabilities in excess of 75md and porosities in excess of 15% and bottom hole pressures in the vicinity of 4000psi.
Description of Propellant-Assisted Perforating
Propellant-assisted perforating techniques have been in use for many years as a method to stimulate completions. Results have been somewhat mixed due to a lack of understanding of the physics involved during the propellant burn event. Advances in the propellant technology have continued to evolve, and these have led to improvements in techniques for well candidate selection, and subsequently, stimulation results. The propellant-assisted perforating technique is used in many different applications with positive results, as described by Boscan ET al.1
The propellant-assisted perforating process combines perforating and perforation breakdown with propellant in a single tool and operation.
Rodrigues, Valdo Ferreira (Petroleos Brasileiro S.A.) | Neumann, Luis Fernando (Petrobras S.A.) | Torres, Daniel Santos (Halliburton Energy Services Group) | Guimaraes De Carvalho, Cesar Roberto (Schlumberger) | Torres, Ricardo Sadovski (BJ Services Do Brasil Ltda.)
This paper presents a brief review of the available techniques in the oil and gas industry to complete and stimulate horizontal wells, with emphasis on low permeability carbonates. These techniques can also be applied in non-conventional reservoirs, particularly in tight formations. The paper starts by reviewing the lessons learned in some chalk fields in the North Sea (Dan, Halfdan, South Arne, Valhall and Eldfisk) and in a few pilot projects offshore Brazil (Congro and Enchova). Based on these lessons learned and in the broad literature, the paper devises some considerations on the methodology to select completion and stimulation techniques for horizontal wells. Cased and cemented horizontal wells, in addition to open hole and perforated/slotted liners wells are addressed. The macro aspects of field/area management are stressed as the completion and stimulation drivers. The key parameters for designing, implementing and evaluating horizontal completion and stimulation are presented, emphasizing the most common failures and the controversial aspects. The paper presents a summary of mature field and new scenarios that are candidate to horizontal completion and stimulation in Brazil and other Latin America countries. Then it makes a few comments on the resources available in Latin America to face the mentioned opportunities and related challenges. It is supposed that this brief review will be useful for the low permeability scenarios in Latin America and worldwide.
This paper presents a brief review of the available techniques in the industry to complete and stimulate horizontal wells, with emphasis on low permeability carbonates. The emphasis on low permeability carbonates in this work is justified by the renewed importance of this scenario in Brazil and other Latin America countries. Although it does not focus on nonconventional reservoirs, such as tight gas, it is related to them as stimulated horizontal completions have been used on their development. This paper focuses fracturing stimulations, also making a few references to matrix stimulation. It also assumes that a horizontal well has already been justified and what is being discussed is its completion and stimulation. The paper starts by reviewing the lessons learned in some chalk fields in the North Sea (Dan, Halfdan, South Arne, Valhall and Eldfisk) and in a few pilot projects offshore Brazil (Congro and Enchova). Then it devises some thought on the methodology used to select completion and stimulation techniques for horizontal wells. It address cased and cemented horizontal wells, in addition to open hole and perforated/slotted liners completions. The key parameters for designing, applying and evaluating horizontal completion and stimulation are presented, underlining the most common failures and the controversial aspects.
Completion and Stimulation of North Sea Low-Permeability Carbonates
The North Sea low permeability chalks are taken here as a reference due to the outstanding technological evolution verified there in the last decades. Amongst more than ten fields producing from these reservoirs in the North Sea this paper focuses on the Dan, Halfdan, South Arne, Valhall and Eldfisk fields. The main characteristics of these fields are: shallow waters (43 to 69 m), dry completion, high volumes of OOIP (1.6 to 2.9 billions barrel), low permeability carbonates (0.2 md to 10 md) with microfractures in the central areas (10 md to 120 md), high porosities (up to 48%), soft to very soft chalks, small to medium net pays (15 m to 65 m), high oil saturation (up to 97%), and light oils ( about 36o API).
What most distinguishes these fields is their over-pressured soft chalks which are subjected to a high degree of compaction under pore pressure depletion, resulting in loss of drilling fluids, rapid production decline, well failures and seafloor subsidence. On the other hand the positive effects of rock compaction as a reservoir drive energy, outweigh by far the negative ones. The recovery factor under primary recovery can be as high as 30%. In general the North Sea chalks experienced an evolution from vertical/directional wells stimulated with acid treatments to multiple fractured horizontal wells.
Technology improvements continue to advance the capabilities of coiled tubing directional drilling (CTDD). Alaska's North Slope, with its prevailing dedication to expanding the technological envelope, has served as a testing ground where advanced CTDD techniques mature into economically viable systems.
Even after over 500 successful CTDD sidetracks on the North Slope, impetus remains to further improve this economical drilling technique. Through a close working relationship between field operator and the service company, significant research and development has led to the introduction of novel tools and services to overcome the intrinsic hurdles of conventional CTDD.
Through a process of miniaturization and innovation, small-diameter systems have been developed for CTDD. The most recent introduction of tools and services includes rib steering technologies, bidirectional wireless mud pulse telemetry, gyro-based MWD services, and ultra-slim, high-resolution, real-time resistivity.
Straighter, longer horizontal laterals, improved steering, and real-time resistivity in openhole sizes as small as 2 3/4-in. ID has been achieved, consequently improving precision in geosteering within the narrowest of payzone.
This paper highlights two case histories describing CTDD technology, real-time formation evaluation, and multilateral drilling processes used to access previously unreachable oil-bearing rock on Alaska's North Slope. While proven in this region, CTDD advances are applicable in other mature fields for the economical extraction of additional reserves.
Ever since CTDD started off in the year 1994 in the North Slope of Alaska, it has become an ongoing desired method for slimhole re-entry from existing wells in the region to access additional reserves. The continuous use of CTDD for re-entry in Alaska, because of the operators' persistent and innovative culture, has made it a proving ground for newer drilling and completion techniques and advanced bottomhole assemblies (BHAs). It has proven itself as the most efficient and cost-effective method of sidetracking and re-entering existing wellbores with cost savings of up to 40% compared to conventional rotary drilling in the region.5
What started off as selecting simple candidates for re-entry with CTDD has now evolved several folds into routine selection of complex candidates presenting just as complex drilling techniques. The vast experience gained in the region and the development of advanced BHAs have made returns from these once "hard candidates?? an economically sound and successful CTDD campaign.
A number of these candidates have an existing 3½-in. tubing, which required the development of advanced tools in sizes as small as 2 3/8-in. to re-enter through these wells without a tubing retrieval operation. The development and usage of these tools in the 2 3/8-in. size redefined the meaning of slimhole drilling and opened up drilling opportunities to many additional wells.1
Key benefits gained from the development of such CTDD tools is the acquired knowledge and experience in re-entry and the drive to push the application into complex and sometimes fragile formations such as those found in the Kuparuk River Unit.
The dynamically overbalanced drilling (DOD) technique-where the drilling fluid is underbalance, yet the surface pressure is adjusted to maintain at-balance condition on bottom-also sometimes known as the managed pressure drilling technique, is a significant improvement in successful drilling technology in such fields. Monitoring of downhole conditions to maintain at-balance conditions, especially the annular pressure, with fastest data update rate, and the ability to steer the BHA as required without any pressure fluctuations were necessary to drill using the DOD technique.2 These BHA requirements apply also to the underbalanced drilling candidates in Alaska.
Fast update rates could only be achieved by an e-line system of steering tools, which had to be in the 2 3/8-in. size to re-enter a number of these complex wells and formations. Hence, the application led to the development of e-line BHAs with downhole dynamics, pressure monitoring, real-time downhole weight on bit, and the functionality to steer and navigate the wellbore in the right path while on bottom drilling.