Cost forecast is the premise and powerful guarantee of cost control. Modern economic activities are becoming increasingly complex and changing rapidly. In order to avoid risks and win in the competition, we must make scientific predictions. Cost prediction should be made before bidding for drilling engineering to facilitate winning the bid; Before construction, the demand and supply of materials and labor force and the construction period must be predicted in order to make a reasonable construction plan.
Drilling engineering cost prediction is a scientific estimation of the future cost level and trend of the project according to the cost information and the specific situation of the project. Drilling engineering can provide decision-making and basis for reducing engineering cost on the premise of meeting the requirements of the owner (or geological design) and itself.
(B) the basic procedures for cost forecasting
The scientific and accurate project cost forecasting program is shown in figure 12-9.
Figure 12-9 Schematic Diagram of Cost Forecasting Procedure of Engineering Project
1. Make a cost forecast plan.
Making a cost forecast plan is the basis to ensure the success of the forecast work. It mainly includes: determining the forecast object, making good organization and deployment, and determining the cooperation department and data collection scope. So as to improve the quality of cost forecasting.
2. Collect and sort out the cost forecast data.
Collecting cost forecast data is an important condition for cost forecast. It is necessary to collect the cost level and related data (stratum, equipment, technology, construction environment, transportation, energy supply, price and consumption of main materials, labor cost, etc.) extensively. ) as the basis of project cost forecast. In the process of collection, the reliability of the data should be analyzed, and the impact of accidental factors and false factors in the data on the cost should be eliminated as much as possible.
3. Selection of cost forecasting methods
There are qualitative and quantitative methods for cost prediction, which can be selected according to the information level of known engineering data. Qualitative prediction is a method to judge the cost according to experience and professional knowledge when the data are insufficient or incomparable (such as the stratum complexity of scientific drilling in Wenchuan earthquake fault zone is rare in China). Quantitative forecasting is a forecasting method to estimate the future cost based on historical data and the quantitative relationship between cost and influencing factors.
4. Preliminary cost forecast
The basis of preliminary cost prediction is qualitative cost prediction and quantitative cost prediction of some horizontal cost data. The results of this forecast are often rough, and need to be further revised in combination with the existing cost level of the project to ensure the quality of the forecast results.
5. Prediction of factors affecting the cost level
The main factors affecting the cost are price, labor productivity, material consumption, indirect expenses and so on. Generally, according to the recent implementation and market situation of similar projects, the factors affecting the project cost in the future can be inferred, and when necessary, uncertainty analysis can be carried out, such as quantity cost analysis, sensitivity analysis and probability analysis.
6. Cost forecast
According to the preliminary cost forecast and the forecast results of cost level change factors, the drilling engineering cost is determined, including labor cost, material cost, machinery use fee and other direct costs.
7. Analyze the prediction error
The result of cost prediction is often different from the actual cost, which leads to prediction error. The analysis of this error is conducive to improving the quality of project cost prediction in the future.
(C) cost forecasting methods
There are three commonly used methods for drilling engineering cost prediction: estimation method, back calculation method and reference method.
1. Cost estimation method
When the complexity of the strata drilled in this project and the drillability of rocks are not clear, and the final hole depth is difficult to determine (only a large range of hole depth is given, and the hole depth is determined according to the geological results obtained during drilling), the cost estimation method is adopted. The cost accuracy of its forecast is relatively poor.
Example: A geological survey project is designed with a single hole depth of1000 m ~ 2,000 m ~ 2,000 m, rock drillability of V ~ ⅸ, unknown formation complexity, final hole diameter ≥ φ 75mm, full hole coring, and drilling quality indicators are implemented according to geological core drilling regulations. Need to calculate the cost of a single hole.
Using the cost estimation method, the calculation is as follows:
1) calculation basis: pre-drilling engineering costs (such as equipment capacity, young crop compensation, water supply, power supply, site leveling, roads, etc. ) according to the maximum hole depth of 2000 meters; The direct cost of construction drilling is used to calculate the final hole depth 1500m. The average drilling rock grade is Grade VIII, and the stratum complexity is moderate. The monthly efficiency of construction platform is estimated by empirical data, and the average monthly efficiency of diamond drilling is determined to be 500m/ month. Consumables and labor costs are estimated at current prices.
2) See table 12-4 for the cost prediction results of estimation method, and table 12-5 for the cost estimation of different intervals. The results show that the constant cost calculated from the maximum hole depth has nothing to do with the actual hole depth, but with the cost composition. The deeper the hole, the lower the proportion of constant cost to total cost, and vice versa. Variable cost and indirect cost have little change with hole depth; In a certain range, the unit cost is higher when the hole is deep and lower when it is deep, but the risk of drilling deep holes is greater. For drilling with a well depth ≥ 1500m, the risks and unforeseen expenses of about 10% ~ 15% should be considered.
Table 12-4 Cost Estimation Results
Table 12-5 Comparison Table of Hole Depth Cost Estimation in Different Interval
Note: The estimated data in the table are based on the estimation standard in table 12-4.
When the comprehensive cost is actually estimated, it should also be included in the national statutory tax and enterprise profits, thus constituting the total cost of the project.
2. Cost back calculation method
When the total cost of drilling project has been determined, the cost back calculation method is a method to calculate all the costs to be invested in the project according to the given hole depth, aperture, formation conditions, engineering quality and time limit requirements, and to predict the costs. This method can predict the cost more accurately with less error, but the total cost should be analyzed, compared, decomposed and evaluated in the calculation process to increase the accuracy of cost prediction. The steps are as follows:
1) Carry out detailed design of drilling construction according to the given conditions;
2) Analyze the one-time drilling construction cost in the total project cost;
3) List all detailed items required for drilling construction;
4) Analyze which are fixed cost expenditure items and which are variable cost expenditure items;
5) Calculate the possible highest cost, regular cost or lowest cost;
6) Evaluate and determine the cost forecast results.
3. Cost reference method
The cost reference method is a method to predict the cost by referring to the recent engineering cost of similar drilling projects (similar areas, strata, hole depth, aperture and engineering quality requirements). Compared with the above two methods, this method has simple calculation and high prediction accuracy.
The cost reference method calculates the forecast value by arithmetically averaging the historical cost data.
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Where: m is the estimated unit cost of the borehole to be built, yuan/meter; DR is the actual value of drilling unit cost r, yuan/m; N is drilling statistics.
For example, 75mm wireline drilling geological exploration boreholes 10 have been constructed in a certain area, and the final hole depth and drilling cost are shown in table 12-6. Try to find the predicted unit cost of drilling with well depth 1800 m in the adjacent area.
Table 12-6 Statistics of Drilling Costs Built
Cost forecast calculation:
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That is, the predicted unit cost of the proposed 1800m deep borehole is 907 yuan /m, and the total cost is about 1632600 yuan.
(D) Cost decision-making
Project cost decision is based on cost prediction, through the analysis and comparison of various feasible schemes, using decision theory to choose the best scheme. Before making a cost decision, a detailed feasibility assessment must be made.
1. Technical feasibility assessment of construction equipment
According to the requirements of the drilling project undertaken, the suitable engineering equipment is carefully selected to ensure the safety, efficiency and economy of the construction. The existing equipment of the unit shall be thoroughly investigated, and the investment and income of the equipment to be increased shall be demonstrated and evaluated. As the saying goes, "Without Jin Gangzuan, we won't do porcelain work". We can't choose the equipment of small horse-drawn carts, and we can't blindly build equipment with insufficient capacity. Otherwise, the construction period will be extended, the cost will increase, and even the construction will not be possible.
After selecting drilling equipment, it is necessary to evaluate whether the technical level of the unit can meet the engineering requirements. If there are shortcomings of 1 ~ 2 in drilling coring, hole inclination control, wall protection and plugging, and deep hole accident treatment, there are certain construction technical risks.
2. Formation complexity assessment
As we all know, drilling into formation plays a key role in drilling difficulty and cost. Therefore, when predicting the cost, we must fully evaluate the complexity of the formation. Avoid mistakes in cost decision-making caused by stratum factors.
3. Unforeseen risk assessment
Drilling is an underground concealed project. In addition to the rising cost of materials and labor, there is also the risk of class change. Unpredictable factors such as wall protection, coring and accidents in holes will greatly increase the cost. Taking a drilling hole with a depth of 3000 meters as an example, it takes as little as ten days and as many as several months to deal with a medium-sized drilling accident, and it costs nearly one million yuan. Therefore, unpredictable risks must be fully considered in the cost prediction and decision-making of drilling engineering.
4. Project yield evaluation
Project yield is the ratio of project net income to total project output value (total investment). Its calculation formula is:
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Where: e is the profit rate of the project; P is the project profit under normal circumstances; I is the total output value (or investment) of the project.
If Eb is the engineering standard rate of return, when E > EB, the project prediction scheme can be implemented.
Example: The total investment of a drilling project is 6,543.8+0,000 yuan, the total expenditure of the project is predicted to be 700,000 yuan, and the unforeseen expenses are 6,543.8+0.5 million yuan. If the standard profit rate EB = 654.38+00%, is it feasible to evaluate and decide the project?
Evaluation calculation:
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E > EB, so the project is feasible.
When evaluating the actual income of the project, we should also consider the investment channels of project funds, the enterprise nature and trustworthiness of investors, and whether the project payment can be paid on time, the interest paid in advance and the possibility of some bad debts after the project is completed. Both are important contents of cost forecasting and decision-making.