Rapid evaluation method for dessert horizon and lithofacies of unconventional oil reservoir

Abstract

The invention discloses a rapid evaluation method for dessert horizon and lithofacies of an unconventional oil reservoir, which is specifically implemented according to the following steps: step 1, drilling core rocks with different depths, and respectively carrying out reservoir characteristic analysis, oil saturation analysis, rock mechanical test, fracture morphology analysis after fracturing and imbibition capability evaluation on the core rocks; obtaining a layer position needing to be subjected to exploration and oil testing; 2, a highly-deviated well is adopted to drill and meet the layer needing exploration and oil testing obtained in the step 1; 3, an armored optical cable is put into the whole shaft in the well cementation process; and step 4, after well completion, performing fracturing treatment on the horizon needing exploration and oil testing, after completion, monitoring well bottom data by adopting an armored optical cable, obtaining production characteristics of various types of lithofacies in each horizon, and judging the sweet spot horizon and the lithofacies according to the production characteristics. The method provided by the invention solves the problem that the sweet spot horizon and sweet spot lithofacies of shale oil with thick longitudinal strata series are slowly understood.

Description

Technical Field

[0001] This invention belongs to the field of oilfield development technology, specifically involving a rapid evaluation method for sweet spots and lithofacies in unconventional oil reservoirs. Background Technology

[0002] "Sweet spots" refer to areas in unconventional formations with relatively high reservoir quality and complex fractures after engineering stimulation. Therefore, identifying sweet spot layers is a crucial step in oil reservoir development. Currently, the common approach is to gradually identify sweet spots by combining laboratory analysis of each layer with field practice. In the field, horizontal wells are typically drilled at a specific target layer requiring vertical alignment. Shale oil is then stimulated through volumetric fracturing and production is initiated. Oil layers are then identified through microseismic monitoring, tracer monitoring, and production fluid analysis. However, this method is slow and time-consuming, thus hindering the pace of unconventional exploration and development. Summary of the Invention

[0003] The purpose of this invention is to provide a rapid evaluation method for sweet spots and lithofacies in unconventional oil reservoirs, which solves the problem of slow identification of sweet spots and lithofacies in shale oil reservoirs with thick vertical strata.

[0004] The technical solution adopted in this invention is a rapid evaluation method for sweet spots and lithofacies in unconventional oil reservoirs, which is implemented according to the following steps:

[0005] Step 1: Drill core rocks at different depths and perform reservoir characteristic analysis, oil saturation analysis, rock mechanics testing, post-compression fracture morphology analysis, and permeability evaluation on the core rocks to obtain the strata that need to be explored and tested for oil.

[0006] Step 2: Drilling with a high deviated angle to encounter the formations in Step 1 that require exploration and oil testing;

[0007] Step 3: During the cementing process, armored optical cables are installed throughout the wellbore.

[0008] Step 4: After well completion, fracturing is performed on the formations that require exploration and oil testing. After completion, armored optical cables are used to monitor the bottom hole data to obtain the production characteristics of each type of lithofacies in each formation. Based on the production characteristics, the sweet spot formations and lithofacies are determined.

[0009] The invention is further characterized in that,

[0010] In step 1, the evaluation parameters for the strata to be explored and tested include lithology and lithofacies, effective porosity, carbonate content, oil saturation, TOC, and fracturing index.

[0011] In step 1, the lithology and lithofacies include layered dolomitic shale and lamellar dolomitic shale.

[0012] In step 2, the inclination of a high-angle well is 60–80°.

[0013] In step 4, production characteristics include daily oil production, formation pressure, and cumulative oil production.

[0014] The beneficial effects of this invention are: This invention provides a rapid evaluation method for sweet spots and lithofacies in unconventional oil reservoirs. It utilizes a high-angle well drilling method to encounter layers requiring exploration and oil testing, and then uses armored optical fibers for data monitoring to evaluate the fracturing effect. This method achieves quantitative evaluation of the production characteristics of different types of lithofacies in different layers during the production process, and achieves the goal of rapidly identifying sweet spots with accurate evaluation results. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of a highly deviated well in the rapid evaluation method for sweet spots and lithofacies in unconventional reservoirs of this invention.

[0016] In the diagram, 1. A well with a high degree of deviation. Detailed Implementation

[0017] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0018] Example 1

[0019] This invention provides a rapid evaluation method for sweet spots and lithofacies in unconventional oil reservoirs, which is implemented according to the following steps:

[0020] Step 1: Drill core rocks at different depths and perform reservoir characteristic analysis, oil saturation analysis, rock mechanics testing, post-compression fracture morphology analysis, and permeability evaluation on the core rocks to obtain the strata that need to be explored and tested for oil.

[0021] The strata requiring exploration and oil testing include Class I and Class II; specific indicators are detailed in Table 1.

[0022] Table 1. Strata and lithofacies type indices requiring exploration and oil testing.

[0023] parameter Class I Category II Lithology and lithofacies Layered dolomitic shale, lamellar dolomitic shale Layered dolomitic shale Effective porosity / % ＞5 3～5 Carbonate content / % ＞45 30～45 Oil saturation / % ≥40 ≥40 TOC / % ＞0.8 0.6～0.8 Fracturability Index / % ＞60 50～60

[0024] Step 2, as follows Figure 1 As shown, a highly deviated well with an inclination of 60-80° was used to drill the formations that needed to be explored and tested in step 1. Using highly deviated wells can produce a fracturing effect similar to that of horizontal wells, ensuring that the effect of the measures during the large-scale development of horizontal wells in the later stage is basically the same as that during the evaluation period, while also ensuring that a sufficient number of formations are encountered.

[0025] Step 3: During the cementing process, armored optical cables are installed throughout the wellbore.

[0026] Step 4: After well completion, the formations that require exploration and oil testing are subjected to fracturing. After completion, armored optical cables are used to monitor the bottom hole data. The monitoring cycle is 0.5 to 1 year to obtain the production characteristics of each formation. In Step 4, the production characteristics include daily oil production, formation pressure, and cumulative oil production. The sweet spot formations and lithofacies are determined based on the production characteristics.

[0027] During the fracturing process, the parameters of each fracturing section are kept consistent to ensure the evaluation of differences between different layers. For fracturing of Class I layers, constant aperture perforation and directional upward 30° perforation are used. For fracturing of Class II layers, constant aperture perforation with a phase angle of 60° is used.

[0028] For the calculation method of using armored optical cables to monitor bottom hole data and obtain production characteristics of each layer, please refer to Duan Jianming, Guo Xiucheng, Zhou Chao. Application and effect analysis of distributed optical fiber fracturing monitoring technology [J]. Inner Mongolia Petroleum and Chemical Industry, 2023, 49(08):81-85.

[0029] Example 2

[0030] Based on Example 1, in step 1, the reservoir characteristics analysis includes porosity, permeability and carbonate content, the rock mechanics test includes uniaxial stress test and geostress test, the post-compression fracture morphology analysis is carried out by rock compression and micro-fracture monitoring experiments, and the uniaxial stress test includes Young's modulus, Poisson's ratio and uniaxial compressive strength.

[0031] In step 1, the percolation capacity was evaluated through an indoor static spontaneous percolation experiment, using distilled water and formation water (mineralization 2.7 × 10⁻⁶). 5 Immersion experiments were conducted using a permeation solution of mg / L and a ratio of formation water to distilled water (1:3). After 15 hours of immersion equilibrium, the core rock was weighed.

[0032] The percolation capacity n is: n=(Δm / ρ) / φV, where Δm is the increase in mass of the sample due to percolation, in g; ρ is the density of the percolated liquid, in g / cm³. 3 φ represents the porosity of the columnar core rock; V represents the volume of the columnar core rock, in cm³. 3 .

[0033] Example 3

[0034] Based on Example 2, the specific process of step 3 is as follows:

[0035] Step 3.1: Prepare for the installation of armored optical cables at the well site, including the placement of the armored optical cable winch, fixing of the optical cable pulley, adjustment of the drilling rig centering, drilling platform preparation, and installation of casing clamps and lifting rings.

[0036] Step 3.2: Lower the armored optical cable into the target location inside the well along with the casing, connect the armored optical cable to the distributed optical fiber temperature testing device, and perform signal detection on the armored optical cable before it enters the well to ensure that the armored optical cable is working properly.

[0037] Step 3.3: Secure the armored optical cable to the conduit, use the armored optical cable conduit clamp protector to secure the end of the armored optical cable, and use steel cable ties to bind the armored optical cable and the conduit body.

[0038] Step 3.4: Lower the armored optical cable into the well along with the casing, release the armored optical cable, control the drilling rig's lowering speed and monitor for obstruction, and conduct signal detection periodically;

[0039] Step 3.5: After the armored optical cable is inserted into the well to the target depth, the pigtail is processed and protected, and an optical cable splice is made. The distributed optical fiber temperature testing device is connected through the optical cable splice to ensure that the well wall distributed optical fiber temperature monitoring system works normally.

[0040] Step 3.6: Perform armored optical cable crossing at the wellhead, modify the annular steel plate, weld the sealing cylinder, cross the armored optical cable, weld the annular steel plate, fill the sealing packing, and add a sealing cap.

[0041] Step 3.7: Perform cementing and continuously monitor the signal fed back by the armored optical cable.

Claims

1. A rapid evaluation method for sweet spots and lithofacies in unconventional oil reservoirs, characterized in that, The specific steps are as follows: Step 1: Drill core rocks at different depths and perform reservoir characteristic analysis, oil saturation analysis, rock mechanics testing, post-compression fracture morphology analysis, and permeability evaluation on the core rocks to obtain the strata that need to be explored and tested for oil. Step 2: Drilling with a high deviated angle to encounter the formations in Step 1 that require exploration and oil testing; Step 3: During the cementing process, armored optical cables are installed throughout the wellbore. Step 4: After well completion, fracturing is performed on the formations that require exploration and oil testing. After completion, armored optical cables are used to monitor the bottom hole data to obtain the production characteristics of each formation. Based on the production characteristics, the sweet spot formations and lithofacies are determined.

2. The rapid evaluation method for sweet spots and lithofacies in unconventional oil reservoirs according to claim 1, characterized in that, In step 1, the evaluation parameters for the strata to be explored and tested include lithology and lithofacies, effective porosity, carbonate content, oil saturation, TOC, and fracturing index.

3. The rapid evaluation method for sweet spots and lithofacies in unconventional oil reservoirs according to claim 2, characterized in that, The lithology and lithofacies include layered dolomitic shale and lamellar dolomitic shale.

4. The rapid evaluation method for sweet spots and lithofacies in unconventional oil reservoirs according to claim 1, characterized in that, In step 2, the inclination of a high-angle well is 60–80°.

5. The rapid evaluation method for sweet spots and lithofacies in unconventional oil reservoirs according to claim 1, characterized in that, In step 4, production characteristics include daily oil production, formation pressure, and cumulative oil production.

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