Research and Application on Intensive Drilling Model of Large Platforms
Authors: Zhao Jianzhong , He Jun , He Yong , Sun Pingtao , Li Yanbo , Chen Hongliang , Zhang Shengliang , Guo Yu 
Published: April 2019

Abstract

Objectives/scope
The poor quality of resources, low utilization of reserves,high investment in capacity building are the main problems faced in low permeability reservoir in Jilin Oilfield.The objective of this research is to form a intensive drilling model of large platforms which can improve the drilling quality,efficiency and management level. By applying this model,we can increase the single well production,block recovery rate and reduce the production construction investments,the development and production costs in low permeability oilfield.

Methods,Procedures,Process
This research based on the production capacity construction in the Jilin Oilfield.This drilling model is different from the traditional model which is inefficient and the investments are higher.Our main procedures included the drilling plan optimization,intensive drilling application,efficient drilling technology application and drilling production management optimization. From 2015 to 2017,we have applied this drilling model successfully in Jilin Oilfield.

Result,Observations,Conclusions
1 Drilling Plan Optimization Technology
The single well and small platforms are commonly used in the reservoir development of Jilin oilfield. Because of the low oil price,we changed our train of thought from traditional development mode to intensive drilling model of large platforms large platforms.It can reduce the land occupation area of well sites,reduce integrated management costs,and improve economical benefits of development effectively.By applying the lowest costs of investment principles,drilling engineering formed integrated drilling plan optimization technology which satisfied the requirements of geological deployment,fracturing and lifting,ground engineering,intensive drilling,economical development.It formed the platform size optimization technology that determined the most economical well number of the platforms.The oil field development investments contain 6 main parts,including drilling engineering,mud log engineering,logging engineering,oil recovery engineering,surface construction engineering and land occupation investments.With the increasing of the platform scale,the investments of drilling engineering increases,because the costs of drilling bits,drilling mud,casing,cement increase,which caused by the increasing of the well depth.The increasing of mud log engineering and logging engineering are not obviously which can be not considered.The investments of oil recovery engineering increases,because the costs of oil lifting,oil pumping machine,well perforation,water flooding increase,which caused by the increasing of the well depth.The investments of surface construction engineering and land occupation investments decrease because of the reduction of well sites pipe network and ground roads.In a word,the investments of drilling and oil recovery engineering increase and the investments of surface construction engineering and land occupation decrease with the increase of platform scale,which exists the optimum interval.By building different models that considering the well vertical depth,well spacing,single well production,platform size,the optimum interval in the main development blocks of Jilin oil field was found out,which is from 16 wells to 25 wells that depends on the reservoir characteristics and development requirements.In the application block,overall drilling plan was optimized from 174 wells on 23 platforms to 87 wells on 2 large platforms,Xinli No.1 and No.2 platform.The subsequent plans contained 8 platforms 116 wells in total which applied this technology.The biggest platforms had 48 wells.There were 4 rows and every row had 12 wells.It also formed the platform drilling plan integrated optimization technology.The wellhead arrangement in the first two platforms was the same as the offshore platforms,which the well site occupation area is the smallest and it is the most convenient to haul the rigs.But the distances of wellhead and row are bigger than the offshore platforms,which can simple drilling procedures.The wellhead distance was 5 meters,and the row distance was 60 meters,which satisfied two drilling rigs and two workover rigs can work at the same time,and the foundation boundary was 30 meters.By applying these technologies,the well site occupation area these two platforms reduced 48.9 thousand square meters in total.In the subsequent plans,the row distance was optimized to 7.5 meters by applying double-well pumping-unit.The well site occupation area were reduced effectively. The standard of platforms well site occupation area were reduced 44%.The area of 10-well-platform was controlled at 0.5 million square meters.
2 Intensive Drilling Application Technology
The common single well and small platforms use one rig to drilling the wells.It has the disadvantages,such as long development cycle,low sharing efficiency of drilling material and oil production pipeline and electric circuit network,which increase production and operation costs and influence construction efficiency.The research formed intensive drilling model which based on the ideas that drilling rigs operated at the same well site,the material and equipment,oil production pipe network,electric circuit network and other resources were shared efficiently.Compared with the single well rig,two to four rigs can shorten the construction period of the platform observably and advance the oil field commissioning.Xinli No.1 and No.2 platform respectively achieved 4 and 3 rigs drilling at the same time by applying the technology including the comprehensive optimization of drilling rig number,well site arrangement,drilling sequence optimization,commissioning schedule optimization,etc.The integral hauling efficiency and accuracy were improved substantially by matching drilling rig fast moving tracks.The integral hauling time was controlled in two hours.The electricity power took the place of the conventional diesel drive power.It had more energy-saving and consumption reduction.It improved the reuse efficiency of drilling materials that drilling fluid reuse rate reached 30%, drill bits and screws were reused 2-3 wells.By applying this mode significantly reduced the overall construction drilling period.Xinli No.1 and No.2 platform drilling period were reduced to 168.2 days and 214.7 days.Xinli No.4-10 platform drilling period were reduced to 117.7 days. The block development efficiency was improved effectively.
3 Efficient Drilling Technology
There are some difficulties in drilling engineering of platform wells,such as drilling anti-collision and avoidance of obstacle well,high risk of well kick and lost circulation.etc.The research formed efficient platform drilling technology typified by the platform well profile optimization,anti-collision,fast and safe drilling,high efficiency cementing.By applying platform well profile optimization technology,the drilling plan satisfied the requirements of geological deployment and adjustment flexibly in large platforms.In the well trajectory optimization,the well location were divided integrally,which the wellheads in outer rows were distributed to the left and right sides of the platform,the wellheads in inner rows were distributed to up and down sides and the middle of the platform.The wellheads were distributed radially row by row and well by well,which made sure the horizontal projection of the well trajectory were not intersected.The wells in outer rows applied the azimuth anti-collision technology that the azimuth of the wells increased gradually to avoid intersection of horizontal projection.The wells in inner rows applied the vertical depth anti-collision technology that the well depth of the KOP increased gradually to avoid intersection of vertical projection.The well depth of the KOP increased by 20 meters well by well and the platform wells adopted the same build rate that was 5.5 degree/30 meters.If the build rate was too small,the well depth was too big that the well drilling investment will increase.If the build rate was too big,the well drilling difficulties will increase.The drilling cycle was nearly the same.So the build rate of 5.5 degree/30 meters can keep the well depth not too big and reduce drilling difficulties and investments.In the anti-collision design,this research applied the 3D closest distance scanning method which can keep anti-collision scanning more reasonable and precise.At the same time,this research formed the anti-collision computation form that was much easier to carry out the anti-collision scanning at the well site.The control measures of well trajectory were formed at the vertical well section,curve section and inclined section.It built the Xinli No.1 platforms that contained 48 wells.By applying anti-collision technology,it guaranteed the construction of Xinli No.1 to No.10 platform smoothly.It achieved zero well lost and the maximum displacement reached 1763 meters.By applying fast and safe drilling technology,the ROP has been increased substantially.The wellbore structure were optimized from composite secondary open hole structure which the upper part borehole diameter was 228.6mm and the lower part borehole diameter was 215.9mm to one trip secondary open hole structure which can simple the drilling structure to shorten drilling cycle,which there was no need to pulling out the drilling tools to change the bit and can drilling from the secondary depth to the total depth.This technology was applied in 9 wells which the drilling cycle was shorten by 16% and there were no additional investment added.In this research,the evaluation of formation drillability was carried out and the drillability grade is from 3-4 in this block.The evaluation of the bits using effect was carried out,and this research formed the bit technical parameters which can satisfy the requirement of drilling speed increasing.Because the formation is easy to drill and the bit wear is less serious,the bits was used in the next wells,which can increase the bit utilization rate, and every bit can drill 3 wells.The BHA was simplified in the research,which used DP to take the place of DC and some DP was placed upside-down in the upper part of the drilling assembly.This design of drilling assembly has the advantage,which the hook load of trip out is the smallest that can reduce the drilling rig load and the hook load of trip in is the biggest that can make the WOB bigger,which can increase the drilling effect. The torque of the rotary table can be reduced by 10%. To solve the problem of high risk of well kick and lost circulation,this research formed the drilling fluid density windows optimization technology and the average and maximum density of the drilling fluids was reduced from 1.51 and 1.72 to 1.46 and 1.65 g/cm3.The proportion of oil-gas-water invasion and drilling loss was reduced from 14% and 13% to7% and 4%.To solve the problem of borehole stability and lubrication and anti-sticking,this research formed the drilling fluid performance optimization technology which the plugging ability and the mud cake quality were improved.By applying this technology,we finished 76 wells that the horizontal displacement was over 500 meters.To solve the problem of cementing in the kick well,this research formed the cementing pressure stabilization technology,including plugging while drilling,pressure test,pad fluid optimization,cement slurry structure optimization,which guarantee the stability of pressure in cementing.To solve the problem of cementing in leakage well,we formed the cementing leak prevention technology,including wellhole preparation,cement slurry density optimization,small displacement cementing construction,low density cementing technology,which prevent cement slurry loss cementing effectively.By applying fast and safe drilling technology,since 2015,the ROP has increased 53%,and the average drilling,completion and construction cycle has reduced by 36%, 33% and 40%,and reached to 6.5 days, 7.8 days and 8.8 days.The proportion of complex conditions was reduced from 15% to 5% in the early stage, which ensured the drilling operation smooth. By applying efficiency cementing technology,the pass rate of cementing reached 100% and the quality rate of cementing reached 82%.
4 Drilling Production Management Optimization
The research formed efficient drilling management model which featured departments including oil company production and operation,engineering technology, scientific research supervisor, drilling construction working together and the specialized and standardized management in drilling design, supervision and technical tackling.The model ensured drilling deployment,design,site construction and follow-up evaluation were operated efficiently.This research also achieved specialized and standardized management in the drilling site.In the preliminary plan designing,the drilling design engineer took part in the every important part such as well site location deployment,well site cushion,drilling rig arrangement,that made the drilling plan can satisfy the construction distance,material transportation,well control requirements,well site emergency.Professional supervisors,supervising director and the head of the construction unit were responsible for drilling site management and supervise,which make sure to find out the problems in time and solve these problems effectively.The supervises of all majors including directional drilling,drilling fluid,cementing carried out the professional supervision and management.The drilling plan can be improved and perfected timely.By applying this drilling production management mode,we achieved all-round supervision and management of the whole drilling cycle.The drilling efficiency and drilling construction quality were enhanced substantially. At the same time,drilling supervision and management level of Jilin oilfield was improved substantially.

Novel/Additive Information
From 2015 to 2018,ten large platforms(over ten wells) has been built.There are 251 wells in all.The number of the biggest platform reaches 48 wells. The success of the research and application on the platform intensive drilling model makes the low permeability reservoirs in Jilin oilfield exploit effectively. It provides new ideas and models for the beneficial development of low permeability reservoirs in Jilin oilfield and CNPC.