Oil & Gas News
Tuesday, 21 April 2009
Drilling Mud Optimisation for Horizontal Offset Wells
Petrov N.A., Korenyako A.V., Davydova I.N., Komleva S.F
When drilling pilot-operational well 1557/22 in the Sugmutskoye field, polymer-clay replenished mud was used as a basis in a horizontal section of the well in the same way as conventional directional wells in Noyabrsk region.
Chemical treatment of the mud included the following materials and chemicals:
Bentonite powder PBMA
The mud was modified via additional treatments with polymers and lubricants (LUB-167 and graphite) and a comprehensive drilling mud surfactant - SNPH-PKD-515. The latter contributed to inhibition (hydration of clay) and surfactant properties. Carbonate heaver was added to increase the mud weight, with Pipe-lax additive in reserve in case of any sticking problems. Following that, a filter (perforated sub) was installed, FSG-146, in a horizontal section. Before sealing the space above the sub with a PDM-146 packer, the drilling fluid, contained in the horizontal section, was displaced with low-concentrated HCl with some cationic surfactant - 0,5-1,5% wetting agent IVV-1.
Oil reservoirs have been developed successfully for quite a while through directional drilling where the horizontal section of a wellbore targets the pay zone. Horizontal wells allow increased oil recovery from a formation due to the following factors:
Drilling and production of horizontal wells began in the Noyabrsk region, particularly in Sugmutskoye field in the early 1990's. This field is in an area of prioritized use of natural resources. Oil deposits were tapped within the field in formation BS 9-2 which represents a complex sand-shale reservoir with West Siberia' generic interlaying of hygrophilous sandstones and mudstones. The roof of the payable formation in the center of the deposit is between 2708 - 2714 m. Waters of BS 9-2 and AC 7 are of the calcium chloride type, with the salinity ranging from 12,10 - 17,03 gr/l. The average formation temperature at the water-oil contact of the formation BS 9-2 is 88C, with a formation pressure of 28.1MPa.
The Senoman deposits of the Sugmutskoye field are not productive. From experience of drilling directional production wells, there is a chance to impair well bore stability, which may result in pipe sticking at intervals above 2700 m. Drilling the interval below the surface casing shoe usually requires utilization of salt-resistant fluids of a polymer-clay nature.
Efficient transportation of cuttings and good carrying capacity of mud are critical factors when drilling wells with a horizontal bottom-hole. Effective transportation of solid particles can be achieved via imparting adequate energy. This provides a turbulent flow with a high velocity. If there is a higher concentration of cuttings in the mud due to a high drill rate, it may exceed the sand-lifting ability of the mud. Therefore, mud velocity in the annulus is regarded as one of the main parameters of bore cleaning. At a very high velocity of turbulent flow, most cuttings may be carried away with the flow. At low velocity, of the stream cuttings may accumulate on the low side of the wellbore wall resulting, eventually, in a cuttings pad on the bottom.
The task of defining what velocity is required to create a turbulent flow in the annulus is difficult. Moreover, turbulent flow should not be created when erosion-sensitive formations are the case, or if the pump is at limited capacity. Rotation of the drilling tool initiates a spiral flow, which in turn assists in cuttings removal and prevents the formation of new layers and sand drifts.
Acceptable levels of well cleaning (with mud) can also be achieved at moderate velocities. For example, at the laminar flow when mud flow characteristics are accurately defined.
Mud flow characteristics (rheology) in a turbulent flow are not linear. Here, there may be concurrently low viscosity and have appropriate carrying capabilities.
High carrying and the thixotropic properties of fluids precludes from the inner sedimentation of solids. At the same time such fluids should contribute to a minimal hydraulic resistance during the course of drilling. This favorably influences the performance of a drill bit.
Cleansing quality at the laminar flow is more sensitive to high viscosity at low gel strength (GS), which should be proportional to the yield point (YP). There is a certain dependency between these values and the quality of cleaning. Experience shows that the YP should be in the region of 30-40dPa, plastic viscosity should stay within 15-20 MPa*s, with relatively low gel strength (gel strength (1) not higher than 10dPa or gel strength (10) not higher than 40dPa). Favorably, funnel viscosity should be kept within 20-30sec.
Adjustment of mud flow characteristics can be done by altering the concentration of the colloidal clay components of mud solids and high-molecular polymer compound.
Stability of bore walls is achieved through adequate mud weight as well as the selection of inhibiting (water repellant) and filtering properties. In particular, fluid loss of polymer-clay mud should be ultimately low, ca. 3-5 cm3/30 min using the BM-6 meter.
The inhibition properties of the filtrate influence the size and properties of the cuttings particles. It is practically good precedure to have a 4-stage mud cleaning programme; in order to enhance performance of the cleaning equipment (mainly a shaker, centrifuge and settling tank) one should use coagulants and flocculants.
The optimal content of solids within the drilling fluid fed into a well bore is 20-22%, including a colloid clay component percentage of 1.6-1.8%. There should be virtually no sand (or it should not exceed 0.5%).
Drilling horizontal sections requires the usage of lubricants that minimize the friction factor between the filter cake and the drill pipe. Drilling fluids successfully used in conventional directional wells serve as a basis that certainly requires modification before drilling a horizontal section.
Polymer-clay types of mud are widely spread in drilling operations in the Noyabrsk region. The chemical composition of drilling mud is mainly the following:
Therefore, the chemical treatment of drilling mud when drilling out from surface casing to 2700 m is performed in accordance with operations procedures applicable for directional drilling. Chemical treatment has a number of features within the highly deviated drilling sections below the intermediate casing shoe (when the building angle is as high as 90%), as well as when drilling a horizontal well in productive formation. In particular, it does the following:
For engineering support of the pilot operational well No. 1557/22 at the Sugmutskoye field (1997) the following procedures of drilling mud preparation and conditioning were planned:
The ejector unit prepares the clay slurry by mixing high quality clay powder, with a density of 1020-1030 kg/m3. The clay-based mud is then mixed with chemicals KMTs-700 or CMC (USA) using 200-250 kg of dry chemical per 100 m3 of drilling fluid. The drilling mud is treated with the chemical CMC, whether in a dry condition or dissolved in water. If it is necessary to replenish the volume of circulation liquid then a water based solution is used, consisting of the chemical CMC and Saipan (Japan) in a ratio of 2:1. The mixture is diluted in a clay mixer on the basis of 2-3 kg CMC, 1,0-1,5 kg Saipan and 1 cubic m of water. Following that, a chemical called Polikem D (Kem-tron, USA) is added to this water composition on the basis of 0.5kg to 1 cubic meter of water.
KMTs-700 chemical is used for lowering fluid loss and adjusting the flow rheology of the mud. Saipan, an Acryl polymer, also reduces fluid loss value and, in addition to this, facilitates well bore stability thanks to its encapsulating (inhibition) effect. The high viscosity of - Polikem D allows a regulated flow rheology of the mud, showing flocculating and inhibiting properties.
In order to achieve both inhibiting, hydrophobic and surfactant properties, the chemical SNPH-PKD-515 was used, which is a composition of non- ionogenic and cation-active surfactants. Complex surfactant blends well with almost all chemicals currently used in the region. The water solution SNPH-PKD -515 is then used to condition drilling mud in a water-agent ratio of 3:1, and is thinly jetted at the pump suction point. Mud conditioning should be started from the interval below the surface casing.
Conditioning with LUB-167, a lubricant from Kem-Тron in the USA, should also start when drilling out from the surface casing and to ensure the concentration of thechemical is maintained in the mud.
Lubricant LUB-167 allows for the efficient reduction of torque, and resistance to the motion of the drilling pipe (drag). Since LUB-167 is a chemical that blends well with almost every chemical used in the region, it can be used in any water-based drilling mud.
For better lubricating mud, it is recommended to additionally use 2-3% graphite for the volume of mud in circulation. Moreover, for well engineering support it is important to have a 200kg reserve of Pipe-lax, an anti-sticking additive made by Kem-tron.
To achieve a higher density of drilling mud to meet procedural parameters, a carbonate heaver should be applied. In order to neutralize Ca2+ions when adjusting pH, 1.5kgs of sodium carbonate per 1 cubic meter of mud can be used.
As the length of the horizontal bore increases, and prior to drilling completion, drilling mud is treated with combined water solution KMTs-700 and Polikem D in a ration of 6:1. The water solution is added evenly throughout circulation cycle.
The operational parameters of drilling mud at intervals between 2700 - 2900 and 2900 - 3100m vertically are presented in the below table.
The sequence of conditioning drilling mud at the above intervals is as follows:
Between 2700 - 2800 meters: drilling mud is treated with the following:
up to 1 ton of KMTs-700 chemical
500 kg of Saipan
100 kg of Polikem D.
5-7 tonnes of preliminary hydrated bentonite powder, type PBMA, then needs to be added for every 100 cubic meters of mud.
During mud circulation 2tonnes of LUB-167 lubricant need to be added, 600 kg of SNPH-PKD-515 surfactant and 20 tonnes of carbonic heaver.
Between 2900 - 3000 meters: At this depth, drilling mud will need to be additionally treated with the following:
400 kg Saipan
400-800 kg of KMTs-700 chemical
up to 50 kg of Police D
up to 700 kg of LUB-167
and up to 600 kg of SNPH-PKD-515.
When drilling a horizontal bore, drilling mud must conditioned with:
2 tonnes of KMTs-700
Up to 700 kg of polymer Saipan
up to 100-150 kg of Polikem D in combination with up to 2 tonnes LUB-167, Up to 1 tonne of graphite
up to 600 kg of SNPH-PKD-515
It is quite logical that during the construction of the first horizontal wells at each field, as a rule, the number of unreliable sections not covered with casing is reduced to minimum.
Thus, for example, before drilling the horizontal section of a well bore an intermediate casing is run into the hole in order to cover the unreliable well bore lengths. Accumulating experience in the construction of sloped and horizontal wells and increasing the quality of drilling mud will ultimately lead to drilling without intermediate casing, which allows for significant savings in capital expenditure.
Indeed, construction of a well with a horizontal offset bears certain risks associated with the potential loss of well bore stability from the moment of drilling-in, untill casing running and cementing. The probability of stability loss of rock is most likely at high inclination angles.
However, rock properties across the geological profile of Sugmutskoye field at high inclination angles has not been studied sufficiently enough. Therefore, at key well No. 1557/22, the plan was to run in an intermediate casing at a maximum vertical depth of 2680m in order to achieve a minimum or zero probability of stability loss in the open hole interval when drilling horizontal section of a well bore.
Since running intermediate casing with a diameter of 245 mm results in a considerable cost increase for horizontal well construction, new data obtained during key-well drilling has enabled operators to optimize the design of other horizontal wells at the Sugmutskoye field.
During the drilling of this well, a new completion program was in effect. The program provided for setting a 146-mm non-cemented casing in a horizontal section with pre-fabricated and installed perforated subs (FSG-146). When running the casing, subs play a role of casing, ensuring the hole circulation through a shoe; and later on, when the well is producing, the subs provide hydrodynamic communications between the productive formation and the well. Before sealing the casing annulus above the horizontal section with packer FSG-146, clay mud in the horizontal bore section is displaced with acid.
The composition of acid solution includes 4-6% of concentrated HCl, with the addition of 0.5-1.5% of water-soluble surfactant cathion (wetting agent NBB-1). Particles of carbonic heaver dissolve under the influence of the acid solution, which in turn restores reservoir permeability. At the same time, the cathion-active additive inhibits the corrosion process on the casing during acid solution injection, inhibits deacidification and hidrophobize pore space at the bottom-hole formation zone, which facilitates cleaning of the bottom-hole formation zone from "impurities" during well flow stimulation.
Because a horizontal well bore section has a non-cemented perforated sub, the quality of tailing-in is, in fact, entirely dependent upon the quality of drilling mud.
In conclusion, when drilling wells with a horizontal offset, special care should be taken when selecting the type of circulation fluid and its composition, as well as when setting an ongoing monitoring process over the parameters of enriched drilling mud. It should also be possible to easily adjust its properties should the need arise.
15:43 0 Comments
KONSTANTIN SOBORNOV - Exploring new frontiers with the EAGE
With the EAGE St.Petersburg taking place in April - what are you looking to achieve through this event?
We hope, as in 2006, that this will be a very successful meeting for all involved. With the current buzz surrounding the regions geo market we hope more people will be find the solutions they seek for their businesses. Basically, we are looking to put the latest technologies from the region and around the world in front of the end users.
What technologies do you think will steal the headlines at this year show?
Well that's a tough question . . . I think that simultaneous pre-stack migration, Q-technologies and sparse surveys are found to be the most important in geophysics - these will be among the technologies to look out for at the show.
With more and more international players looking to enter the regions geophysical sector, how do you see them integrating with local Russian competitors?
There are different methods to get integrated in the Russian geophysical sector and different companies chose different strategies. It looks likely that partnership with Russian companies may be a good option and we see more and more international companies taking this route.
What major investments are planned for exploration in 2008? And are there any state incentives for growth in this area?
Investments into exploration are numerous with most majors planning some sort of exploration spend. It also seems that the State is going to accelerate exploration in East Siberia to make sure that sufficient amount of oil is available the East Siberia - Pacific Ocean pipeline. It is a tremendously ambitious project which needs a lot of investments, hard work and luck in exploration and related activities
What regions do you see as being a hotbed of exploration activity in the coming couple of years?
Aside from East Siberia mentioned in the previous answer, a number of areas will prove to be exploration "hotbeds" in the coming years including Timan-Pechora, offshore Far East and Caspian - I think these areas are likely to of key interest in terms of exploration.
With the Russian artic being touted as the final frontier for hydrocarbon exploration, will the harsh and remote environment hold back exploration studies?
On the contrary, as I know almost all major oil companies are involved in studies of exploration potential of the Russian Arctic.
Of course explorers are going to face the most difficult, sensitive and challenging environment ever found, let's not forget the difficulties of working in such conditions. But despite these issues, interest in the hydrocarbon potential of this area will grow massively, providing new and exiting opportunities for regional majors and providing a huge market to the local and international geo-industry.
Even with such interest and potential, it will take no less than a decade to evaluate the full potential of this area.
Is there a demand for geophysical technologies on current brown field sites?
Demand for geophysical technologies in brown field developments will be on the rise for years to come. This is due mainly to the current state of affairs in brown field site and of course the strong oil price.
How will the marketplace have changed before EAGE St.Petersburg 2010 takes place?
I think it is clear that exploration developments are on the rise and that the oil business will be supporting many of us by EAGE 2010 and well beyond.
The Russian oil industry will become more consolidated and quality G&G services will be in greater demand with many new and exiting projects underway. Additionally the development of Russia's harsh and sensitive regions, a lot more emphasis will be placed on correct geo technology development.15:23 0 Comments
Mike Davies, President of Baker Hughes Russia, talks technology, strategy and outlook.
1. Operators are under increasing governmental pressure regarding environmental and tax compliance. What effect, if any, is this having on Baker Hughes's strategy for the region?
Baker Hughes has a global program that we have labeled "Completely Compliant", or we train 100% of our employees in Russia and around the globe what "Completely Compliant" means. It means complete compliance with all laws, both laws of the Russian Federation and other jurisdictions that apply, as well as compliance with our Health, Safety & Environmental Management System, and our Core Values. We work hard to ensure the health and safety of our employees and to be a responsible corporate citizen, not harming the environment.
We conduct regular and meticulous environmental and safety audits of our facilities. We pay our taxes promptly and properly declare the value of any imported goods or equipment.
From a business standpoint our Fluids Environmental Service (FES) provides safe handling and disposal of drilling fluids and waste cuttings.
2. At present there is a shortage of qualified personnel within the OFS market in Russia. Is recruitment of the relevant talent proving challenging?
This is a top issue for the industry in general and one which we face daily. Baker Hughes is growing very rapidly in Russia. Our number of employees, 98% Russian-speaking, has more than tripled in the past 18 months. This places a huge strain on the organization's ability to maintain our corporate culture and impart the level of skill needed to provide the excellent execution at the well-site that Baker Hughes is known for worldwide.
In response to this challenge we have taken several actions. First, we have geared up our graduate recruitment and cooperation programs with oil and gas faculties at leading Russian universities. Second, we have or will be commissioning training facilities in Noyabrsk and Tyumen to conduct both technical and non-technical training. Third, we have formal Employee Development and Succession Planning processes that identify areas of needed skill development and help develop actionable plans to fill the gaps. Fourth, this year we are sending some of our future leaders on foreign assignments to develop broader skills, learn new technologies and network into the global Baker Hughes organization. And fifth, we have begun looking outside the Russian Federation for Russian-speaking service technicians to help support our business growth.
3. Which product/technology line offered by Baker Hughes Russia do you feel will have the biggest impact in the region during the course of the next year to eighteen months?
There are many opportunities for Baker Hughes technologies to add value. A few of the more significant ones include:
4. Russian Service companies are investing more and more into R&D in an attempt to compete with Western companies such as Baker Hughes. Do you feel the competition is hotting up?
We see the increased competition as a positive sign for the industry. Baker Hughes intends to build for the long-term in Russia. We have established a research center in Novosibirsk, where we do basic geoscientific research. We are evaluating expanding the scope of our own local R&D efforts. We feel there is opportunity for Baker Hughes to develop products specifically for the local markets here. That has been a critical strength of Baker Hughes' over our 100-year history, and we plan to apply that same approach in Russia. Ultimately, this approach gives our customers the best solutions at the most efficient cost.
5. How do you see the OFS market developing in Russia over the next decade?
The forthcoming decade will continue to be an exciting one for the oilfield service industry in Russia. We believe that the consolidation within our industry will continue. Some of the VIOC's have reiterated their plans to divest their in-house OFS units via trade sales or IPO's. Interest in acquiring smaller, and regionally based service providers will remain high, and Baker Hughes will consider such acquisitions seriously.
At the same time, our clients will place increasing emphasis on green field developments, featuring complex geologies and remote locations. Given the higher spread costs compared to the brownfields of Western Siberia, we expect the focus of evaluation to shift more to cost-in-use rather than tendered price. Service providers will continue to find ways to effectively apply both new and existing technologies to help contain the escalating cost per ton of production.
6. What role do you see Baker Hughes Russia taking?
Baker Hughes Russia will continue to develop as a major service and technology provider to our clients in the Russian Federation. We expect to be among the industry consolidators. We continue to invest in the infrastructure needed to support world-class operations. We will compete in all market tiers.15:13 0 Comments