Application of new geosteering technology in thin reservoir

: Because some oilfields in China belong to the thin bottom water reservoir model, the actual drilling process is technically difficult. In order to ensure the maximum drilling operation of the target layer and the basic development effect of the oilfield, technicians should introduce advanced steering tools and study new geosteering technology to fundamentally ensure the exploitation quality of thin oil reservoirs.After exploring the introduction of new geological guidance technology in detail, this paper further explores the principle of new geological guidance technology, and summarizes the application strategy of new geological guidance technology combined with the development of thin-layer reservoir.


Introduction
The sandstone reservoir of an oil field in China is a typical bottom water structural reservoir, so the reservoir thickness is relatively low and the bottom water energy of oil and gas field is sufficient, so it is necessary to use horizontal well development technology.During the implementation of the new geological guidance technology, it mainly refers to the detailed exploration of the detection technology of wellhead trajectory based on the core conditions of basic geological research, aiming at the trajectory curve of drilling and exploration well, combined with the relevant data of downhole drilling, so as to give full play to the basic role of geological guidance technology, and combined with the drilling conditions, geological conditions The downhole curve predicts the structural change of the target layer, and timely adjusts the wellhead trajectory, so that the well body can cross the reservoir structure to the greatest extent.

Introduction to New Geosteering Technology
In the process of thin-layer reservoir exploitation, the new-type geosteering technology is developed on the basis of the guiding drilling technology, and with the continuous improvement of scientific and technological level, the application scope of the new-type geosteering technology is expanding.In the 1960s, enterprises have successfully developed natural gamma technology and resistivity detection technology, but remote sensing detection technology is still in the primary stage.This detection status leads to serious constraints and restrictions on the performance and function of downhole equipment.
Since the 1980s, the MWD/LWD technology has gradually matured, and the guided drilling technology has officially entered the exploitation of thin reservoirs, this situation has led to various types of geological information detection equipment, such as: electromagnetic induction resistivity detection equipment, neutron porosity detection equipment and formation density detection equipment, etc. , although the geological guidance equipment used in this period can meet the needs of a small part of geological structure exploration, it still can not carry out precise exploration for special geological conditions.In recent years, with the continuous use of geological steering drilling technology, the basic functions of downhole steering equipment and instruments have been continuously improved and optimized, and bit geological drilling equipment have emerged one after another, such as EWR / ABI, DGR / ABI, etc.This exploration status also leads to the continuous research and production of various geological survey equipment with comprehensive functions and excellent operation performance.During this period, the new geological guidance technology and equipment have been growing rapidly and can evaluate the geology in real time and comprehensively.At this time, the geological guidance drilling technology has officially entered the peak development period.At present, more technicians are developing and exploring in an all-round way the more excellent Rotary Guidance Technology and closed-loop guidance technology on the basis of the already mature geological guidance technology, in the process of thin-layer reservoir exploitation, rotary steering and closed-loop steering will become the main E3S Web of Conferences 358, 02025 (2022) https://doi.org/10.1051/e3sconf/202235802025GESD 2022 steering technology of exploration technology, which is widely used in various geological conditions.As shown in Table 1, the type of horizontal well and the Oriented Technical Model [2].

Principle of new geological guidance technology
In the process of thin layer oil reservoir production, the new geosteering technology is mainly divided into two modes, such as SST and MWD/DWD, in which SST guiding equipment mainly provides technical support for downhole equipment through cable lines, in this way, the real-time collection of downhole reservoir data can be transmitted to the ground receiving equipment according to certain data and information patterns, and the ground structure instrument can decode and process the received signals in detail, finally, the accurate downhole data is displayed on the display equipment.As shown in Table 2, instrument comparison.When MWD/DWD technology is used for directional drilling and information measurement, it mainly uses mud or formation medium, and uses downhole detection equipment to carry out core information measurement or drilling operation, it is necessary to take out the downhole detection equipment and repeat the above construction and measurement process according to the project construction, but the equipment can not be effectively placed at the bottom of the well in the section with large displacement parameters or drilling angle, then need to use the opening pump to the bottom of the well, the opening pump base key and other construction technology.As shown in Figure 1, the implementation process of new geological guidance technology.

Development of thin layer reservoir
In the actual energy development of thin layer reservoirs in a certain area of China, due to the special local natural environment and geological conditions, the reservoirs can not be effectively developed and used.First, the reservoir foundation depth in this area is small, and the internal structure of the rock is very dispersed and loose.The shallowest landfill depth of the oil layer is only about 1700 meters underground, and the maximum energy depth is only about 1900 meters underground.Therefore, relatively little information and data are available.Under the background of incomplete data, it is impossible to get the drilling fluid structure system which matches the local formation better, and the Rock Structure Dispersion has put forward a higher technical requirement for bit equipment selection and operation technology.Second, because the oil reservoir in this area belongs to thin geological structure, the oil layer is thin.The maximum oil layer thickness is only about 10m, while the minimum oil layer thickness is 3M, so the average oil layer in this area is no more than 5m.For this kind of thinlayer reservoir, when actually developing energy, each horizontal well should be controlled and managed by three location points, and the external shape of the horizontal development section needs to ensure bow shape, and the length of the construction section in the horizontal direction should be controlled at about 800m.Since the reservoirs in this area are bottom-water reservoir models, it is important to ensure that the entire horizontal section is kept away from the reservoir layer at the oil-water interface and that the excavation length is 1.2-1.4m from the top of the soil layer, therefore, the orbit control of this class is relatively difficult.Third, at present, the non-uniform characteristics of the vertical stratum of the thin-layer reservoir are relatively high, so the geological structure of the reservoir fluctuates greatly, which is very easy to produce obvious structural fluctuations in local positions.Therefore, when using the geological guidance technology, it is required to be close to the top of the sand and gravel soil layer, so as to ensure a high level of drilling success rate.The base oil layer of an oil field in China is relatively thin, its average oil layer thickness is about 5 meters, so the oil field belongs to a typical thin layer oil reservoir, and the oil reservoir types in this area are mainly bottom water oil reservoirs, for this reason, during the actual development of an oil field, the project development needs to be carried out for a horizontal well, and the specific location of the horizontal section should be located at the top of the oil field about 1 meter, away from the interface between the oil and water resources at all times, ensure that the basic productivity of Horizontal Wells, the specific location of horizontal wells concentrated in the top of the oil.When using the new geological guidance technology, due to the great impact of the oilfield hard interlayer on the landing, once the landing angle is too large, the rebound problem will occur at the interface when using the bit, resulting in the bit falling back into the soil and rock structure again.If the hard interlayer rock is relatively thick, even if the bit lands successfully, the angle will also be too large, resulting in the long-time drilling operation of the bit in the hard interlayer, resulting in serious wear of the bit equipment.If the hard interlayer is too thin, the vertical depth of the horizontal well will be lower because of the too small angle, which will affect the dynamic movement mode of the oil well [4] .Therefore, it is necessary to divide the landing mode of bit equipment carefully according to the actual situation of hard interlayer at the top of oil layer.If there is a hard interlayer at the top of the oil layer, the landing angle should be about 86-87 degrees, and the drilling speed should be controlled effectively during the actual drilling process, make sure that the deviation is gradually increased throughout the drilling process, so that the angle between the bit and the geological stratum can reach about 88-89 degrees after the bit penetrates the hard interlayer.

Operation cases
Due to the changes of geological structure and sedimentary environment in this area, the soil covered above the oil field shows a certain regularity.Therefore, during reservoir exploitation, it is necessary to use drill bits to distinguish in detail according to the changes of soil and rock distribution, and predict the specific landing depth in combination with the geological data of this area.Taking the A14 horizontal well as a practical case, it is necessary to distinguish the horizontal well from its own structure and the data of adjacent wells before drilling, and to divide at least 3 marked structural layers above the final exploration target structural layers, after drilling a marked layer, the drill bit needs to compare the actual drilling depth and angle with the expected measurement, which can be used as the basis to adjust the guidance parameter model and predict the landing depth.Because the sedimentary structure of the oil field in this area causes obvious changes in the local geological position, when the bit is drilled vertically to about 1700m, it is basically consistent with the scheme design.After drilling to the lower layer for re measurement and calculation, it is significantly different from the depth of the target landing layer.In addition, the changes and uncertainties caused by the local geological structure directly affect the production quality of the oil field, Therefore, if the drill bit wants to encounter the target layer, it needs to adjust the angle to drill at least 10m depth, and the drilling angle reaches more than 88 degrees, so the landing effect is ideal.As shown in Figure 2, downhole cross section.Technology oriented operating principles Since the oilfield is mainly a thin-layer bottom water reservoir, the geological stratum has sufficient water resources.In order to ensure that the drilling trajectory is always below the soil, rock and hard interlayer, it is necessary to stay away from the oil-water boundary in the horizontal section, and drill part of the oil layer structure above the vertical direction as far as possible, so as to ensure the basic productivity in the horizontal well, If there is a clay or calcareous interlayer below the oil layer, it cannot pass through the interlayer.

Case Study
In the process of drilling operation, on the one hand, the influence of seismic information on geological structure should be controlled as a whole, and on the other hand, the results of downhole detection curve should be analyzed and judged in detail, and on the basic conditions of comprehensive study, it can effectively judge the underground construction trajectory and the actual realtime position, and carry out the trajectory adjustment and control according to the situation of oil reservoir production, for this reason, well A11 should be taken as a practical case for the implementation of new geosteering technology.Because the base thickness of the oil layer in this horizontal well is about 4 meters, and the geology of this section belongs to thin sandstone reservoir, in general, the upper part of this geological oil layer will develop a mud interlayer structure with a thickness of about 1 meter, so horizontal well trajectory control, we need to choose the sudden intercalation and 1-1.5 meters between the top of the oil layer, and as close as possible to the top of the soil structure.When the drill bit is used to drill an oil well, the drilling angle should be controlled at about 87 degrees, and the maximum angle increases to about 90 degrees with the deepening of the drilling depth.After the drill bit is used to drill to 2400m, the gamma parameters generated by the drill bit will gradually increase.This situation directly shows that with the increasing depth of the drill bit, Soil quality and foundation content are increasing.At the same time, the resistivity and soil oil content are decreasing and decreasing.
According to the density curve of soil top structure, with the increase of drilling depth, the density of soil top structure shows an increasing trend, to this end, the technicians have combined the relevant data and information, such as Gamma Ray, resistivity and density curves, to further explain that the increase in drilling depth will result in the drilling location near the top of the soil and rock, the drilling angle should then be reduced to 89 degrees and the wellhead trajectory should be returned to the sandstone formation as far as possible.
Because the rock structure of the horizontal well is very scattered and loose, it is relatively difficult to control the well deviation.Therefore, it is necessary to continuously increase or reduce the well deviation angle to ensure that the bit can drill stably.The length of horizontal well is 860 meters, the effective length of horizontal section is 815 meters, and the vertical depth of drill bit should be controlled below 1 meter in order to ensure the quality of thin layer reservoir production.As shown in Fig. 3, downhole curve test chart [5].

Conclusion
It can be seen that in the process of thin-layer reservoir exploitation, the new geological guidance technology has become the key factor for the success of drilling, fundamentally ensuring the smooth landing of horizontal well drilling, better controlling the connecting track of horizontal section, and realizing the objectives of detecting geological structure.

Fig. 1
Fig. 1 implementation flow of new geosteering technology

Table 1
Types of horizontal wells and oriented technical models