(Urumqi 8300 1 1, Planning and Design Institute of Northwest Petroleum Bureau)
Drilling fluid technology for deep horizontal wells is a comprehensive technology, which mainly considers borehole wall stabilization technology, borehole wall purification technology, high temperature stabilization technology and lubrication anti-sticking technology. MMH polysulfonate mixed oil and composite metal ion polysulfonate mixed oil drilling fluid system are mainly used in horizontal wells in Tahe Oilfield. The author mainly introduces the field application technology, maintenance and application effect of the two systems.
Key words: drilling fluid borehole purification, borehole stable lubrication and reservoir temporary plugging technology
1 overview
With the deepening of exploration and development in Tahe Oilfield, in order to improve the development well pattern and increase oil and gas productivity, 7 horizontal wells have been deployed in Tahe Oilfield 1 Well and Well 2. The oilfield is located in Shaya Uplift in Tarim Basin, with deep oil and gas reservoirs, and the drilled depths are all around 4,500m, with complicated geological conditions. The sandstone and mudstone of Kuqa Formation, Kangcun Formation and Jidike Formation of Paleogene are interbedded with unequal thickness, with weak cementation, poor diagenesis, good drillability, high sandstone permeability and strong mudstone hydration dispersion. Lower Jurassic and Triassic mudstones are mainly composed of illite (36% ~ 60%), containing 65,438+05% illite/montmorillonite. The mixed layers are orderly (S accounts for 22%), and some intervals contain 65,438+05% illite/montmorillonite, and the mixed layers are disordered (S accounts for 50%). Mudstone is generally not easy to disperse when it meets water, but there are: ① hard and brittle shale bedding and micro-cracks are developed, and mudstone is easy to hydrate, expand and disperse, resulting in high expansion pressure, which leads to wall peeling and collapse; ② Abnormal pore pressure of mudstone and high collapse pressure caused by strong geostress are easy to cause mechanical instability. The pressure of liquid column is lower than that of mudstone formation, and the hydration of the same formation is quite different. The pressure coefficient of mudstone formation is higher than that of oil layer, and the stress on the borehole wall is unbalanced.
The upper layer is easy to cause shrinkage and blockage of virtual thick sand mud cake and viscous drilling cuttings mud cake, and the drilling fluid must have strong coating, strong inhibition ability, good wall-building and lubricity. The denuded block in the lower layer collapsed seriously, the borehole wall became unstable, and the borehole diameter was enlarged, which was in the deviated and horizontal interval. Drilling fluid must have effective anti-sloughing measures. At the same time, due to the particularity of deep horizontal wells, such as high bottom hole temperature, complex lithology of strata, deep deflection point and horizontal section, anti-sticking and anti-collapse, high requirements for logging and cementing, and large amount of drilling fluid, it is difficult to maintain and adjust, and there are many engineering accidents.
2 drilling fluid technical requirements
In horizontal well drilling, the main problems are that the drill string inclines to the lower borehole wall in the inclined section and sinks eccentrically, and the contact area between the drill string and the borehole wall increases, which leads to the increase of downhole friction coefficient. Difficulties in carrying rocks: the downward direction of cuttings is changed from the axial downward direction of vertical wells to the radial downward direction of inclined wells and horizontal sections. It is difficult to overcome the radial downward force of drilling cuttings by axially lifting drilling fluid. Under normal circumstances, sediments will inevitably form in inclined wells, and the thickness of sediments will increase with the increase of dip angle. The deposition of drilling cuttings on the lower borehole wall leads to the destruction of the suspension uniformity of drilling fluid, which is not conducive to carrying drilling cuttings and increases the friction resistance between the drill string and the borehole wall. In the strata with well-developed bedding, sandstone, conglomerate and complex strata with poor cementation are prone to collapse and block falling, and in serious cases, drilling tools will be buried, resulting in sticking. To sum up, drilling fluid is required to have strong lubricity, rock carrying capacity, anti-sloughing capacity and wellbore stability. Well depth in this area requires good temperature resistance of drilling fluid. Reservoir protection is more important for drilling fluid in horizontal interval.
3 drilling fluid design
3. 1 borehole cleaning technology
By improving the plastic viscosity, dynamic shear force, dynamic-plastic ratio and static shear force of drilling fluid, drilling fluid has good suspension carrying capacity and high dynamic-plastic ratio and shear force, thus reducing the settling speed of drilling cuttings and bringing them out in time. MMH positive gel and composite metal ion polymer (PMHC) were selected to adjust the rheology of drilling fluid, which ensured the proper annular velocity, not only protected the borehole wall, but also played the role of carrying rock. Foreign research indicates that when the inclination angle of annulus is in the whole range of 0 ~ 90, the greater the flow rate of drilling fluid, the higher the purification speed of annulus. In horizontal wells, stick to rotating drilling tools regularly and tripping in short distances. Rotary drilling is beneficial to remove drilling cuttings. First, the cuttings deposited on the lower borehole wall are pushed into the flowing drilling fluid and carried out of the borehole by the drilling fluid flow. Secondly, grinding large cuttings into small particles is beneficial to the suspension of cuttings out of the borehole. Controlling borehole trajectory can reduce flow resistance and kinetic energy consumption, which is beneficial to removing drilling cuttings. In addition, according to the wellbore structure and drilling tool assembly, choosing appropriate annular return rate and rheological parameters of drilling fluid can not only ensure rock carrying, but also reduce erosion damage to unstable wellbore.
3.2 borehole wall stabilization technology
In view of the mineral composition, physical and chemical characteristics and wellbore instability of Jurassic and Triassic shales, firstly, the drilling fluid must have low filtration rate and good mud cake quality, which can effectively plug layered microfracture shales in a short time; Secondly, there should be enough inhibition to effectively prevent the borehole wall from swelling and collapsing due to water absorption, and at the same time prevent the cuttings from dispersing and reduce the solid content; In addition, the proper annular velocity of drilling fluid is controlled to reduce the erosion of drilling fluid to the borehole wall. Therefore, the efficient anti-sloughing inhibitor and polysulfonate mixed oil drilling fluid system were optimized, and reasonable anti-sloughing technical measures were taken to meet the requirements of horizontal deep well drilling construction. Use asphalt products such as FT- 1, SMP, SPNH, NH4PAN and other plugging anti-sloughing agents to mechanically plug bedding and cracks, increase the plugging ability of drilling fluid, reduce water loss and mud cake permeability, and prevent drilling fluid filtrate from entering the formation in large quantities. SN- 1 solid emulsifier with strong oil absorption is used to participate in the formation of mud cake, forming a hydrophobic oil film on the borehole wall, effectively controlling filtrate invasion and reducing mudstone hydration. Long-chain and high-molecular polymers have strong ionic groups, polar groups and nonpolar groups, which adsorb, bridge and flocculate with clay surface, thus coating mudstone and inhibiting clay dispersion. At the same time, the anti-sloughing and fluid loss agent PA- 1 is applied to improve the chemical inhibition ability of drilling fluid, restrain the hydration and dispersion of shale to the maximum extent and prevent the borehole wall from collapsing. PA- 1 is a graft copolymer of KHm and cationic components. K+ and cationic components cooperate to improve the anti-collapse effect, and the addition of cations improves the adsorption and hydration ability.
3.3 Lubrication anti-interference technology
According to the specific situation of drilling construction in Tahe Oilfield, referring to the relevant technical data at home and abroad, after comprehensive analysis and research, the method of mixing crude oil is selected to improve the lubrication performance of drilling fluid. At the same time, the solid emulsifier SN- 1 is selected as the emulsifier, and its molecular structure contains cationic groups with strong lipophilicity and anionic groups with good hydrophilicity, which has amphiphilic effect. After adding SN- 1 into the oil-mixed drilling fluid, the oil can be fully absorbed, and the oil can be enriched by SN- 1 to participate in the formation of mud cake, forming an oil film with emulsified droplets on the surface of mud cake, and transforming the friction between drilling tools and mud cake or borehole wall into the friction between drilling tools and oil film, which can greatly reduce friction resistance and torque. Through laboratory experiments, the reasonable addition amounts of crude oil and SN- 1 solid emulsifier were optimized to be 8% ~ 10% and 0.3% ~ 0.5% respectively, and the recommended on-site crude oil addition amount was 10% ~ 12%. In addition, in order to improve the lubricity of drilling fluid, under special circumstances, 2% ~ 3% plastic particle solid lubricant is added and semi-buried in the mud cake to form micro-support between the mud cake and the drilling tool or casing, which acts as a "micro-bearing" to avoid differential pressure sticking and reduce torque and friction resistance.
3.4 Oil and gas reservoir protection
According to the research and analysis results of reservoir characteristics and damage mechanism, that is, the reservoir is not weak in water sensitivity, and the invasion and pollution of solid particles are the main factors of reservoir damage caused by drilling and completion fluid. In order to adapt to the characteristics of drilling strata and the special requirements of deep horizontal well construction and make the construction technology simple, the water-based drilling and completion fluid system is optimized from the aspects of economy, operability and oil and gas reservoir protection, and the shielding temporary plugging technology is implemented to protect oil and gas reservoirs, so as to keep the solid phase and filtration as low as possible. On the basis of the upper composite metal ion polysulfonate mixed oil drilling fluid, MMH positive gel polysulfonate mixed oil and composite metal ion polysulfonate mixed oil are used to temporarily plug the drilling and completion fluid system.
In addition to the above factors, drilling fluid design should also consider vertical intervals, especially long open-hole intervals in the second and third spudding intervals, and mudstone and sandstone interbeds. Mudstone section is easy to be filled with mud, and thick mud cake in sandstone section is easy to cause sticking. The drilling fluid should maintain low solid content, strong inhibition, thin and tough mud cake and good lubricity to ensure safe and rapid drilling. Potassium-based polymer drilling fluid system and positive gel drilling fluid system are mainly used in the first spudding and the second spudding, while the third spudding mainly uses positive gel polymer mixed oil temporary plugging drilling fluid system and composite metal ion polysulfonate mixed oil temporary plugging drilling fluid system, and each system is reformed in turn. The composite metal ion polymer non-dispersion system and positive gel drilling fluid system have strong inhibition and low solid phase characteristics, which are suitable for fast drilling in middle and upper layers. The drilling fluid system and polysulfonate system for temporary plugging with positive gel polymer mixed oil have the characteristics of high temperature resistance, low water loss at high temperature and high pressure and good wall-building, and are suitable for drilling in the lower interval. At the same time, it is suitable for drilling oil and gas intervals.
The compound metal ion polysulfonate mixed oil drilling fluid system formula: (40 ~ 50) kg/m3 bentonite +(2 ~ 3) kg/m3 soda ash+(3 ~ 4) kg/m3 NaOH+(2 ~ 5) kg/m380a51+2kg/m3 pmhc+20kg/m3smp-650.
The formula of positively charged polymer drilling fluid system: (40 ~ 50) kg/m3 bentonite +(2 ~ 3) kg/m3 soda ash+(5 ~10) kg MMH+(5 ~10) kg/m3 PAM+(2 ~ 4) kg/m3 PAC-H.
4 Introduction to Drilling Engineering
All the 7 horizontal wells drilled were run with 244.5mm technical casing, and then the directional drilling was carried out with 2 15.9mm bit. See table 1 for basic data of construction engineering.
Table 1 Basic Data of Horizontal Well Drilling in Tahe Oilfield
sequential
5 Drilling fluid field application technology
5. 1 borehole wall stabilization technology
During drilling, the anti-collapse measures of mudstone section are as follows: Mechanically, in order to improve the support of drilling fluid column pressure to the borehole wall and make it greater than the collapse density of the formation, the use density of drilling fluid is 1.20 ~ 1.22g/cm3, which is 0.02 ~ 0.05g/cm3 higher than the normal use density of the same horizon of the completed straight wells in this area, and the uniqueness of drilling fluid is considered. Chemically, MMH positive gel, PA 1, WFT-666, FT- 1, SPNH, SMP- 1, PMHC and NH4-PAN are mainly supplemented to improve the quality of mud cakes and enhance the ability of drilling fluid to inhibit, plug and prevent formation collapse. At the same time, the special function of SN- 1 solid emulsifier to adsorb crude oil and form an oil film on the borehole wall is used to improve the borehole stability. In addition, the filtration rate can be reduced, so that the water loss of API is below 4ml and that of HTHP is 9 ~ 10 ml, thus reducing the immersion depth of the borehole wall and laying a foundation for long-term safe construction.
5.2 Lubrication technology
The lubrication performance of drilling fluid is mainly crude oil. When the angle of inclination reaches 30 and enters the horizontal interval, crude oil 18t and 12t are added to make the oil content of drilling fluid and drilling and completion fluid 8% ~ 10%, and a certain amount of SN- 1 solid emulsifier (or SP-80) is added for full emulsification, supplemented by 2%. The filter cake friction coefficient Kf is always controlled below 0.029, the tripping resistance is generally 4t~8t ~ 8 t, and the rotating torque is 300 ~ 450 mv.
5.3 Drilling Purification Technology
Drilling fluid and drilling and completion fluid with strong carrying capacity of suspended rock are mainly selected. Under low flooding, MMH positive gel (or PMHC) and NH4PAN gel are mainly supplemented, and the viscosity and rheology are adjusted so that the dynamic shear force is greater than 15 Pa, the dynamic-plastic ratio is about 1, and the initial cutting is generally 18 ~ 23 Pa, and the initial cutting is close to the final cutting. In the project, measures such as short tripping and rotating drilling tools were taken in time. During the construction of the well, tripping, logging and pipe plugging were all completed at one time, and the pump was started normally, which ensured that the whole horizontal section did not run into the well at one time, but everything was normal underground, and no obvious cuttings returned after large-displacement well washing, which proved that the well was clean and no obvious cuttings bed was formed.
5.4 Reservoir Protection Technology
Before entering the horizontal section, fully adjust the drilling fluid performance, control the low solid content and filtration loss, add 0.75% ~ 1.0% oil-soluble resin and 3% QS-2 to the disposable mixing funnel periodically, add sulfonated asphalt to make the content reach 2% ~ 3%, implement shielding and temporary plugging technology to protect oil and gas reservoirs, and replenish them in time according to consumption. Further strengthen the quality of mud cake and reduce the amount of filtrate invading the oil layer. At the same time, strengthen borehole purification and solid phase control, reduce the particles in drilling fluid from entering the pay zone pores, and avoid blocking oil and gas channels.
5.5 Solid phase control
Solid phase control is mainly based on vibrating screen, cleaner and centrifuge. Frequent tripping operations bring certain difficulties to the control of drilling fluid density and solid content and the maintenance of performance. Therefore, effective measures have been taken, such as making full use of the existing solid control equipment, increasing the supplementary amount of colloidal solution, improving the rock carrying capacity of drilling fluid, reducing the degree of repeated grinding, and reducing the content of fine particles, so as to control the sand content within 0.2% and the solid content within 1 1% ~ 13%.
6 field application effect
Seven wells have been drilled in Tahe Oilfield, and MMH positive colloid polysulfonate mixed oil drilling fluid and composite metal ion polysulfonate mixed oil drilling fluid are mainly used in the construction, each of which has its own characteristics in field use. During drilling, TK 106H and TK20 1H are accident-free wells, and other wells are stuck to varying degrees. Its performance is shown in Table 2. MMH positive gel polysulfonate mixed oil drilling fluid has poor temperature resistance and is difficult to maintain and treat in deep wells. Due to the poor compatibility of MMH positive adhesive with other types of treatment agents, the use of anionic treatment agents weakened the positive charge of the system, thus reducing the anti-collapse ability of the system. However, MMH positive gel system has strong rock carrying capacity, which prevents the formation of "cuttings bed" and ensures smooth tripping. The composite metal ion polysulfonate mixed oil drilling fluid has good temperature resistance, compatibility, rheology and stable performance.
Application of MMH positive gel system in wells 6. 1, TK 104H and tk201h.
Before drilling in this interval, the drilling fluid is converted into MMHSN-2 drilling fluid system in the casing to make the MMH content reach 3% (colloid). Due to the serious block falling in the upper stratum of this well section, 3% PN- 1 and 2%FT- 1 anti-sloughing agent were added into the casing at one time, 8% crude oil was mixed into the deviated well section, and enough solid emulsifier Sn-66 was added.
When the angle of inclination reaches 60, strengthen short-distance tripping and grading circulation, increase the YP of drilling fluid to above 15Pa, control the dynamic-plastic ratio between 0.8- 1.2, and increase the static shear force to 8-10pa/10-/kloc-. Make full use of four-stage solid control equipment and the method of adding glue solution to reduce the sand content of drilling fluid and meet the design requirements.
Stable drilling fluid performance, suitable rheology, strong anti-sloughing ability and low friction coefficient, and cooperation with engineering measures are the keys to the success of this interval.
(1) φ 6 reading is not less than 8.5.
(2) In the construction process, maintenance is given priority to, treatment is supplemented, and drilling fluid treatment agent is added in the form of glue to keep the performance of drilling fluid stable.
Table 2 Drilling fluid performance of deviated wells and horizontal intervals Table 2 Field performance of deviated wells and horizontal intervals
(3) Adjust the drilling fluid flow pattern with SPNH and NH4-HPAN; Control of high temperature and high pressure water loss with SMP- 1 and SPNH.
Reasonable compatibility of various treatment agents, good lubricity, strong anti-sloughing ability and hanging ability are the keys to the success of drilling fluid in this well.
6.2 application of composite metal ion polysulfonate mixed oil system in well TK202h
Before orientation, polymer drilling fluid is converted into composite metal ion polysulfonate mixed oil drilling fluid at one time. Add 40m3 of pre-prepared new slurry (1.5t bentonite +80kg Na2CO3+50kg NaOH+75kg pmhc). Then, while circulating according to the formula, evenly add SPNH, FT- 1, SMP- 1, PA- 1 and PMHC with a mixing funnel, and then add an appropriate amount of Na2CO3. After the circulation is relatively uniform, 8% crude oil is mixed uniformly in large circulation, and 0.3%SN- 1 solid emulsifier is added at the same time. Finally, fully circulate until the drilling fluid performance is basically stable.
In the process of drilling, we always insist on the maintenance of supplementary glue. The maintenance principles of drilling fluid performance are: paying attention to borehole purification, controlling rheological property, maintaining appropriate high dynamic-plastic ratio and shear force to meet the special needs of carrying cuttings and effectively suspending cuttings, controlling the quality and lubricity of mud cakes, strengthening anti-sloughing measures and strictly controlling water loss. The selection and supplement of various treatment agents vary with normal drilling footage, lithology, inclination angle and operating conditions encountered during drilling. Generally speaking, the replenishment time of glue solution is within 1 ~ 2 weeks before each drilling.
6.3 Conclusion and understanding
Due to the effective and reasonable drilling fluid maintenance and treatment technology adopted in the deflecting section and horizontal section of horizontal well, the drilling fluid has excellent performance and good construction effect. The drilling fluid properties are shown in Table 2.
(1) The drilling fluid has strong rock carrying capacity in suspension and the borehole is clean.
The drilling fluid has the characteristics of positive gel, good rock carrying effect, strong suspension ability and normal cuttings return, and can normally bring out cuttings suspended before the last trip on time every time; The cuttings are uniform, especially in the highly inclined section and horizontal section, without mixing layers, with pure texture and clear edges and corners, reflecting clear stratigraphic boundaries, and the interpretation results of cuttings logging and electrical logging are consistent.
(2) The drilling fluid has good sloughing resistance, stable borehole wall and regular borehole diameter.
During the whole construction process, although there are many trips and the bottom hole conditions change greatly, the borehole wall is stable due to the excellent drilling fluid performance, reasonable technical measures and less shale peeling during drilling cycle, and there is no borehole wall collapse and instability. The screen of vibrating screen basically screens out cuttings, and each stroke is smooth and there is no abnormality. The average hole diameter expansion rate is shown in Table 3, which well solves the common problems of Triassic hard brittle shale formation.
Table 3 Comparison of Bore Diameter of Third spudding Section of Horizontal Well in Tahe Oilfield Table 3 Comparison of Bore Diameter of Third spudding Section of Horizontal Well in Tahe Oilfield
(3) The drilling fluid has good lubrication performance.
Due to the special function of SN- 1 solid emulsifier, reasonable crude oil content and good solid phase control effect, the mud cake of drilling fluid is thin and tough, and the friction coefficient is low. Kf is always controlled between 0.0 143 ~ 0.029, so that friction and torque are minimized. Drilling and tripping are smooth, electrical logging and screen pipe running are unimpeded, the friction of tripping is generally 4 ~ 8 t, and the torque is 300 ~ 400 mv.
(4) The drilling fluid has stable performance and is easy to maintain and adjust.
In the whole construction process, although the drilling time is short and tripping is frequent, only simple maintenance and glue adjustment are needed for each drilling trip, without large-scale treatment.
(5) Drilling fluid has a good protective effect on oil and gas reservoirs.
Reasonable implementation of shielding and temporary plugging technology to protect oil and gas reservoirs has small filtration loss, API water loss is less than 4.0ml, and high temperature and high pressure water loss is kept at 9 ~ 1 1.0 ml. The indoor evaluation results show that the average recovery value of the core permeability of the composite metal ion polysulfonate mixed oil drilling and completion fluid system is 92.2%, which not only plays a good role in protecting oil and gas reservoirs, but also achieves the function of leakage prevention and plugging.
(6) The composite metal ion polysulfonate mixed oil drilling fluid has stable performance and easy maintenance, and is an ideal drilling fluid system for horizontal well drilling.
refer to
[1] Fan Shizhong, Yan Jienian, Zhou. Drilling fluid, completion fluid and reservoir protection technology. Dongying: Petroleum University Press, 1996.
Xu Tongtai, Chen Leliang, Luo Pingya. Deep well mud. Beijing: Petroleum Industry Press, 1994.
Shao-Huai Chang, Luo Pingya, etc. Reservoir protection technology. Beijing: Petroleum Industry Press, 199 1.
Drilling fluid technology for horizontal wells in Tarim basin
Jin Shubo Kimberly Wen Bin
Planning and Design Institute of Northwest Petroleum Geology Bureau? rümqi 8300 1 1)
Abstract: Drilling fluid for deep horizontal wells should focus on borehole stability technology, borehole purification technology, high temperature stability technology, lubrication and sticking prevention technology. Oil-mixed MMH polymer sulfur and oil-mixed recovery of lubricating ionic polymer sulfur were used in horizontal wells in Tahe Oilfield. This paper introduces the field application and effect of the two systems.
Keywords: drilling fluid borehole fine borehole stable lubrication reservoir protection temporary plugging technology